OrCAD PSpice user`s guide

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Pspug.book Page 1 Wednesday, November 11, 1998 1:14 PM
OrCAD PSpice®
User’s Guide
Pspug.book Page 2 Wednesday, November 11, 1998 1:14 PM
Copyright © 1998 OrCAD, Inc. All rights reserved.
Trademarks
OrCAD, OrCAD Layout, OrCAD Express, OrCAD Capture, OrCAD PSpice, and
OrCAD PSpice A/D are registered trademarks of OrCAD, Inc. OrCAD Capture CIS,
and OrCAD Express CIS are trademarks of OrCAD, Inc.
Microsoft, Visual Basic, Windows, Windows NT, and other names of Microsoft
products referenced herein are trademarks or registered trademarks of Microsoft
Corporation.
All other brand and product names mentioned herein are used for identification
purposes only, and are trademarks or registered trademarks of their respective
holders.
Part Number 60-30-636
First edition 30 November 1998
Technical Support
Corporate offices
OrCAD Japan K.K.
OrCAD UK Ltd.
Fax
General email
Technical Support email
World Wide Web
OrCAD Design Network (ODN)
9300 SW Nimbus Ave.
Beaverton, OR 97008 USA
(503) 671-9400
(503) 671-9500
81-45-621-1911
44-1256-381-400
(503) 671-9501
[email protected]
[email protected]
http://www.orcad.com
http://www.orcad.com/odn
Pspug.book Page iii Wednesday, November 11, 1998 1:14 PM
Contents
Before you begin
xxiii
Welcome to OrCAD . . . . . . . . .
OrCAD PSpice overview . . . . . .
How to use this guide . . . . . . . .
Typographical conventions . .
Related documentation . . . . . . .
Online Help . . . . . . . . . . .
If you have the demo CD-ROM
OrCAD demo CD-ROM . .
What’s New . . . . . . . . . . . . .
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xxiii
xxiv
. xxv
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xxvi
xxvii
xxviii
xxviii
. xxix
Chapter overview . . . . . . . . . . . . . . . . .
What is PSpice? . . . . . . . . . . . . . . . . . .
Analyses you can run with PSpice . . . . . . . .
Basic analyses . . . . . . . . . . . . . . . . .
DC sweep & other DC calculations . . .
AC sweep and noise . . . . . . . . . . .
Transient and Fourier . . . . . . . . . . .
Advanced multi-run analyses . . . . . . . .
Parametric and temperature . . . . . . .
Monte Carlo and sensitivity/worst-case
Analyzing waveforms with PSpice . . . . . . .
What is waveform analysis? . . . . . . . . .
Using PSpice with other OrCAD programs . . .
Using Capture to prepare for simulation .
What is the Stimulus Editor? . . . . . . . .
What is the Model Editor? . . . . . . . . . .
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Part one
Simulation primer
Chapter 1
Things you need to know
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Contents
Files needed for simulation . . . . . . . . . . . . . . .
Files that Capture generates . . . . . . . . . . . .
Netlist file . . . . . . . . . . . . . . . . . . . . .
Circuit file . . . . . . . . . . . . . . . . . . . .
Other files that you can configure for simulation
Model library . . . . . . . . . . . . . . . . . . .
Stimulus file . . . . . . . . . . . . . . . . . . .
Include file . . . . . . . . . . . . . . . . . . . .
Configuring model library, stimulus, and
include files . . . . . . . . . . . . . . .
Files that PSpice generates . . . . . . . . . . . . . . .
Waveform data file . . . . . . . . . . . . . . .
PSpice output file . . . . . . . . . . . . . . . .
Chapter 2
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13
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Chapter overview . . . . . . . . . . . . . . . . . . . . . . .
Example circuit creation . . . . . . . . . . . . . . . . . . . .
Finding out more about setting up your design . . . .
Running PSpice . . . . . . . . . . . . . . . . . . . . . . . . .
Performing a bias point analysis . . . . . . . . . . . . .
Using the simulation output file . . . . . . . . . . . . .
Finding out more about bias point calculations . . . .
DC sweep analysis . . . . . . . . . . . . . . . . . . . . . . .
Setting up and running a DC sweep analysis . . . . . .
Displaying DC analysis results . . . . . . . . . . . . . .
Finding out more about DC sweep analysis . . . . . .
Transient analysis . . . . . . . . . . . . . . . . . . . . . . .
Finding out more about transient analysis . . . . . . .
AC sweep analysis . . . . . . . . . . . . . . . . . . . . . . .
Setting up and running an AC sweep analysis . . . . .
AC sweep analysis results . . . . . . . . . . . . . . . .
Finding out more about AC sweep and noise analysis
Parametric analysis . . . . . . . . . . . . . . . . . . . . . . .
Setting up and running the parametric analysis . . . .
Analyzing waveform families . . . . . . . . . . . . . .
Finding out more about parametric analysis . . . . . .
Performance analysis . . . . . . . . . . . . . . . . . . . . .
Finding out more about performance analysis . . . . .
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Simulation examples
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Contents
Part two
Design entry
Chapter 3
Preparing a design for simulation
55
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Checklist for simulation setup . . . . . . . . . . . . . . . . . . . . .
Typical simulation setup steps . . . . . . . . . . . . . . . . . . .
Advanced design entry and simulation setup steps . . . . . . .
When netlisting fails or the simulation
does not start . . . . . . . . . . . . . . . . . . . . . . . .
Things to check in your design . . . . . . . . . . . . . . . .
Things to check in your system configuration . . . . . . . .
Using parts that you can simulate . . . . . . . . . . . . . . . . . . .
Vendor-supplied parts . . . . . . . . . . . . . . . . . . . . . . .
Part naming conventions . . . . . . . . . . . . . . . . . . . .
Finding the part that you want . . . . . . . . . . . . . . . .
Passive parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Breakout parts . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Behavioral parts . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using global parameters and expressions for values . . . . . . . .
Global parameters . . . . . . . . . . . . . . . . . . . . . . . . . .
Declaring and using a global parameter . . . . . . . . . . .
Expressions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Specifying expressions . . . . . . . . . . . . . . . . . . . . .
Defining power supplies . . . . . . . . . . . . . . . . . . . . . . . .
For the analog portion of your circuit . . . . . . . . . . . . . . .
Defining stimuli . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Analog stimuli . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Using VSTIM and ISTIM . . . . . . . . . . . . . . . . . . . .
If you want to specify multiple stimulus types . . . . . . .
Things to watch for . . . . . . . . . . . . . . . . . . . . . . . . . . .
Unmodeled parts . . . . . . . . . . . . . . . . . . . . . . . . . .
Do this if the part in question is from the OrCAD libraries
Check for this if the part in question is custom-built . . . .
Unconfigured model, stimulus, or include files . . . . . . . . .
Check for this . . . . . . . . . . . . . . . . . . . . . . . . . .
Unmodeled pins . . . . . . . . . . . . . . . . . . . . . . . . . . .
Check for this . . . . . . . . . . . . . . . . . . . . . . . . . .
Missing ground . . . . . . . . . . . . . . . . . . . . . . . . . . .
Check for this . . . . . . . . . . . . . . . . . . . . . . . . . .
Missing DC path to ground . . . . . . . . . . . . . . . . . . . .
Check for this . . . . . . . . . . . . . . . . . . . . . . . . . .
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Contents
Chapter 4
Creating and editing models
85
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . . .
What are models? . . . . . . . . . . . . . . . . . . . . . . . . .
Models defined as model parameter sets . . . . . . . .
Models defined as subcircuit netlists . . . . . . . . . .
How are models organized? . . . . . . . . . . . . . . . . . . .
Model libraries . . . . . . . . . . . . . . . . . . . . . . . . .
Model library configuration . . . . . . . . . . . . . . . . .
Global vs. design models and libraries . . . . . . . . . . .
Nested model libraries . . . . . . . . . . . . . . . . . . . .
OrCAD-provided models . . . . . . . . . . . . . . . . . . .
Tools to create and edit models . . . . . . . . . . . . . . . . . .
Ways to create and edit models . . . . . . . . . . . . . . . . . .
Using the Model Editor to
edit models . . . . . . . . . . . . . . . . . . . . . . . . .
Ways to use the Model Editor . . . . . . . . . . . . . . . .
Model Editor-supported device types . . . . . . . . . . . .
Ways To Characterize Models . . . . . . . . . . . . . . . .
Creating models from data sheet information . . . . .
Analyzing the effect of model parameters
on device characteristics . . . . . . . . . . . . .
How to fit models . . . . . . . . . . . . . . . . . . . . . . .
Running the Model Editor alone . . . . . . . . . . . . . . .
Starting the Model Editor . . . . . . . . . . . . . . . . .
Enabling and disabling automatic part creation . . . .
Saving global models (and parts) . . . . . . . . . . . .
Running the Model Editor from the schematic page editor
What is an instance model? . . . . . . . . . . . . . . . .
Starting the Model Editor . . . . . . . . . . . . . . . . .
Saving design models . . . . . . . . . . . . . . . . . . .
What happens if you don’t save the instance model . .
The Model Editor tutorial . . . . . . . . . . . . . . . . . . .
Creating the half-wave rectifier design . . . . . . . . .
Using the Model Editor to edit the D1 diode model . .
Entering data sheet information . . . . . . . . . . . . .
Extracting model parameters . . . . . . . . . . . . . . .
Adding curves for more than one temperature . . . .
Completing the model definition . . . . . . . . . . . .
Editing model text . . . . . . . . . . . . . . . . . . . . . . . . .
Editing .MODEL definitions . . . . . . . . . . . . . . .
Editing .SUBCKT definitions . . . . . . . . . . . . . . .
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Contents
Changing the model name . . . . . . . . . . . . . . . . .
Starting the Model Editor
from the schematic page editor in Capture . . . . .
What is an instance model? . . . . . . . . . . . . . . . .
Starting the Model Editor . . . . . . . . . . . . . . . . .
Saving design models . . . . . . . . . . . . . . . . . . .
Example: editing a Q2N2222 instance model . . . . . . . . .
Starting the Model Editor . . . . . . . . . . . . . . . . .
Editing the Q2N2222-X model instance . . . . . . . . .
Saving the edits and updating the schematic . . . . . .
Using the Create Subcircuit command . . . . . . . . . . . . . .
Changing the model reference to an existing model definition .
Reusing instance models . . . . . . . . . . . . . . . . . . . . . .
Reusing instance models in the same schematic . . . . . . .
Making instance models available to all designs . . . . . .
Configuring model libraries . . . . . . . . . . . . . . . . . . . .
The Libraries and Include Files tabs . . . . . . . . . . . . . .
How PSpice uses model libraries . . . . . . . . . . . . . . .
Search order . . . . . . . . . . . . . . . . . . . . . . . . .
Handling duplicate model names . . . . . . . . . . . . .
Adding model libraries to the configuration . . . . . . . . .
Changing design and global scope . . . . . . . . . . . . . .
Changing model library search order . . . . . . . . . . . . .
Changing the library search path . . . . . . . . . . . . . . .
Chapter 5
Creating parts for models
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111
112
112
113
114
114
114
115
115
117
118
118
119
120
120
121
121
122
122
123
124
125
127
Chapter overview . . . . . . . . . . . . . . . . . .
What’s different about parts used for simulation?
Ways to create parts
for models . . . . . . . . . . . . . . . . . .
Preparing your models for part creation . . . . .
Using the Model Editor to create parts . . . . . .
Starting the Model Editor . . . . . . . . . . . .
Setting up automatic part creation . . . . . .
Basing new parts on a custom set of parts . . . .
Editing part graphics . . . . . . . . . . . . . . . .
How Capture places parts . . . . . . . . . . .
Defining grid spacing . . . . . . . . . . . . . .
Grid spacing for graphics . . . . . . . . .
Grid spacing for pins . . . . . . . . . . . .
Attaching models to parts . . . . . . . . . . . . .
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129
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Pspug.book Page viii Wednesday, November 11, 1998 1:14 PM
Contents
MODEL . . . . . . . . . . . . . . . . . . . . .
Defining part properties needed for simulation
PSPICETEMPLATE . . . . . . . . . . . . . .
PSPICETEMPLATE syntax . . . . . . . .
PSPICETEMPLATE examples . . . . . .
Chapter 6
viii
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138
139
140
140
143
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . .
Overview of analog behavioral modeling . . . . . . . . . . .
The ABM.OLB part library file . . . . . . . . . . . . . . . . .
Placing and specifying ABM parts . . . . . . . . . . . . . . .
Net names and device names in ABM expressions . . .
Forcing the use of a global definition . . . . . . . . . . .
ABM part templates . . . . . . . . . . . . . . . . . . . . . . .
Control system parts . . . . . . . . . . . . . . . . . . . . . . .
Basic components . . . . . . . . . . . . . . . . . . . . . .
Limiters . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chebyshev filters . . . . . . . . . . . . . . . . . . . . . . .
Integrator and differentiator . . . . . . . . . . . . . . . .
Table look-up parts . . . . . . . . . . . . . . . . . . . . .
Laplace transform part . . . . . . . . . . . . . . . . . . .
Math functions . . . . . . . . . . . . . . . . . . . . . . . .
ABM expression parts . . . . . . . . . . . . . . . . . . .
An instantaneous device example: modeling a triode . .
PSpice-equivalent parts . . . . . . . . . . . . . . . . . . . . .
Implementation of PSpice -equivalent parts . . . . . . .
Modeling mathematical or instantaneous relationships .
EVALUE and GVALUE parts . . . . . . . . . . . . .
EMULT, GMULT, ESUM, and GSUM . . . . . . . . .
Lookup tables (ETABLE and GTABLE) . . . . . . . . . .
Frequency-domain device models . . . . . . . . . . . . .
Laplace transforms (LAPLACE) . . . . . . . . . . . . . .
Frequency response tables (EFREQ and GFREQ) . . . .
Cautions and recommendations for simulation and analysis
Instantaneous device modeling . . . . . . . . . . . . . .
Frequency-domain parts . . . . . . . . . . . . . . . . . .
Laplace transforms . . . . . . . . . . . . . . . . . . . . . .
Non-causality and Laplace transforms . . . . . . . .
Chebyshev filters . . . . . . . . . . . . . . . . . . . .
Frequency tables . . . . . . . . . . . . . . . . . . . . .
Trading off computer resources for accuracy . . . . . . .
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147
148
149
150
150
151
152
153
155
156
157
160
160
164
167
168
171
174
175
176
176
178
179
181
181
183
186
186
187
187
188
190
190
191
Analog behavioral modeling
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147
Pspug.book Page ix Wednesday, November 11, 1998 1:14 PM
Contents
Basic controlled sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . 192
Creating custom ABM parts . . . . . . . . . . . . . . . . . . . . . . . 192
Part three Setting Up and Running Analyses
Chapter 7
Setting up analyses and starting simulation
195
Chapter overview . . . . . . . . . . . . . . . . . . . . . . .
Analysis types . . . . . . . . . . . . . . . . . . . . . . . . .
Setting up analyses . . . . . . . . . . . . . . . . . . . . . .
Execution order for standard analyses . . . . . . . . .
Output variables . . . . . . . . . . . . . . . . . . . . . .
Modifiers . . . . . . . . . . . . . . . . . . . . . . . .
Starting a simulation . . . . . . . . . . . . . . . . . . . . .
Starting a simulation from Capture . . . . . . . . . . .
Starting a simulation outside of Capture . . . . . . . .
Setting up batch simulations . . . . . . . . . . . . . . .
Multiple simulation setups within one circuit file .
Running simulations with multiple circuit files . .
The PSpice simulation window . . . . . . . . . . . . .
Chapter 8
Chapter 9
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195
196
197
198
199
200
206
206
207
207
207
208
208
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DC Sweep . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum requirements to run a DC sweep analysis . . . . . . . .
Overview of DC sweep . . . . . . . . . . . . . . . . . . . . . . . . .
Setting up a DC stimulus . . . . . . . . . . . . . . . . . . . . . . . .
Nested DC sweeps . . . . . . . . . . . . . . . . . . . . . . . . . . .
Curve families for DC sweeps . . . . . . . . . . . . . . . . . . . . .
Bias point . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum requirements to run a bias point analysis . . . . . . . .
Overview of bias point . . . . . . . . . . . . . . . . . . . . . . . . .
Small-signal DC transfer . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum requirements to run a small-signal DC transfer analysis
Overview of small-signal DC transfer . . . . . . . . . . . . . . . . .
DC sensitivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum requirements to run a DC sensitivity analysis . . . . . .
Overview of DC sensitivity . . . . . . . . . . . . . . . . . . . . . . .
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213
214
214
216
218
219
221
223
223
223
225
225
226
228
228
229
DC analyses
AC analyses
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213
231
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231
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Pspug.book Page x Wednesday, November 11, 1998 1:14 PM
Contents
AC sweep analysis . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setting up and running an AC sweep . . . . . . . . . . . . . .
What is AC sweep? . . . . . . . . . . . . . . . . . . . . . . . .
Setting up an AC stimulus . . . . . . . . . . . . . . . . . . . .
Setting up an AC analysis . . . . . . . . . . . . . . . . . . . . .
AC sweep setup in example.opj . . . . . . . . . . . . . . . . .
How PSpice treats nonlinear devices . . . . . . . . . . . . . .
What’s required to transform a device into a linear circuit
What PSpice does . . . . . . . . . . . . . . . . . . . . . . .
Example: nonlinear behavioral modeling block . . . . . .
Noise analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Setting up and running a noise analysis . . . . . . . . . . . . .
What is noise analysis? . . . . . . . . . . . . . . . . . . . . . .
How PSpice calculates total output
and input noise . . . . . . . . . . . . . . . . . . . .
Setting up a noise analysis . . . . . . . . . . . . . . . . . . . .
Analyzing Noise in the Probe window . . . . . . . . . . . . .
About noise units . . . . . . . . . . . . . . . . . . . . . . .
Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Chapter 10
Transient analysis
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232
232
232
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235
237
239
239
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241
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242
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242
243
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246
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249
250
250
250
250
252
252
253
253
254
254
256
256
257
259
260
260
260
260
261
249
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . . .
Overview of transient analysis . . . . . . . . . . . . . . . . . .
Minimum requirements to run a transient analysis . . . .
Minimum circuit design requirements . . . . . . . . .
Minimum program setup requirements . . . . . . . .
Defining a time-based stimulus . . . . . . . . . . . . . . . . .
Overview of stimulus generation . . . . . . . . . . . . . .
The Stimulus Editor utility . . . . . . . . . . . . . . . . . . . .
Stimulus files . . . . . . . . . . . . . . . . . . . . . . . . . .
Configuring stimulus files . . . . . . . . . . . . . . . . . .
Starting the Stimulus Editor . . . . . . . . . . . . . . . . .
Defining stimuli . . . . . . . . . . . . . . . . . . . . . . . .
Example: piecewise linear stimulus . . . . . . . . . . .
Example: sine wave sweep . . . . . . . . . . . . . . . .
Creating new stimulus symbols . . . . . . . . . . . . . . .
Editing a stimulus . . . . . . . . . . . . . . . . . . . . . . .
To edit an existing stimulus . . . . . . . . . . . . . . .
To edit a PWL stimulus . . . . . . . . . . . . . . . . . .
To select a time and value scale factor for PWL stimuli
Deleting and removing traces . . . . . . . . . . . . . . . .
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Pspug.book Page xi Wednesday, November 11, 1998 1:14 PM
Contents
Manual stimulus configuration . . . .
To manually configure a stimulus
Transient (time) response . . . . . . . . . .
Internal time steps in transient analyses .
Switching circuits in transient analyses . .
Plotting hysteresis curves . . . . . . . . . .
Fourier components . . . . . . . . . . . . .
Chapter 11
Chapter 12
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261
261
263
265
266
266
268
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Parametric analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum requirements to run a parametric analysis . . . . . . .
Overview of parametric analysis . . . . . . . . . . . . . . . . . .
RLC filter example . . . . . . . . . . . . . . . . . . . . . . . . . .
Entering the design . . . . . . . . . . . . . . . . . . . . . . . .
Running the simulation . . . . . . . . . . . . . . . . . . . . .
Using performance analysis to plot overshoot and rise time .
Example: frequency response vs. arbitrary parameter . . . . . .
Setting up the circuit . . . . . . . . . . . . . . . . . . . . . . .
Temperature analysis . . . . . . . . . . . . . . . . . . . . . . . . . . .
Minimum requirements to run a temperature analysis . . . . . .
Overview of temperature analysis . . . . . . . . . . . . . . . . . .
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271
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281
281
282
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288
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293
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297
297
Parametric and temperature analysis
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271
Monte Carlo and sensitivity/worst-case analyses
283
Chapter overview . . . . . . . . . . . . . . . . . . . . . .
Statistical analyses . . . . . . . . . . . . . . . . . . . . . .
Overview of statistical analyses . . . . . . . . . . . .
Output control for statistical analyses . . . . . . . . .
Model parameter values reports . . . . . . . . . . . .
Waveform reports . . . . . . . . . . . . . . . . . . . .
Collating functions . . . . . . . . . . . . . . . . . . .
Temperature considerations in statistical analyses .
Monte Carlo analysis . . . . . . . . . . . . . . . . . . . .
Reading the summary report . . . . . . . . . . .
Example: Monte Carlo analysis of a pressure sensor
Drawing the schematic . . . . . . . . . . . . . . .
Defining part values . . . . . . . . . . . . . . . .
Setting up the parameters . . . . . . . . . . . . .
Using resistors with models . . . . . . . . . . . .
Saving the design . . . . . . . . . . . . . . . . . .
Defining tolerances for the resistor models . . .
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xi
Pspug.book Page xii Wednesday, November 11, 1998 1:14 PM
Contents
Setting up the analyses . . . . . . . . . . . . .
Running the analysis and viewing the results
Monte Carlo Histograms . . . . . . . . . . . . . .
Chebyshev filter example . . . . . . . . . . . .
Creating models for Monte Carlo analysis . .
Setting up the analysis . . . . . . . . . . . . .
Creating histograms . . . . . . . . . . . . . . .
Worst-case analysis . . . . . . . . . . . . . . . . . . .
Overview of worst-case analysis . . . . . . . . . .
Inputs . . . . . . . . . . . . . . . . . . . . . . .
Procedure . . . . . . . . . . . . . . . . . . . . .
Outputs . . . . . . . . . . . . . . . . . . . . . .
Caution: An important condition for
correct worst-case analysis . . . . . . .
Worst-case analysis example . . . . . . . . . . . .
Tips and other useful information . . . . . . . . .
VARY BOTH, VARY DEV, and VARY LOT .
Gaussian distributions . . . . . . . . . . . . .
YMAX collating function . . . . . . . . . . . .
RELTOL . . . . . . . . . . . . . . . . . . . . .
Sensitivity analysis . . . . . . . . . . . . . . .
Manual optimization . . . . . . . . . . . . . .
Monte Carlo analysis . . . . . . . . . . . . . .
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299
300
301
301
302
302
303
306
306
307
307
308
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308
309
313
313
314
314
314
314
314
315
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . . .
Overview of waveform analysis . . . . . . . . . . . . . . . . .
Elements of a plot . . . . . . . . . . . . . . . . . . . . . . .
Elements of a Probe window . . . . . . . . . . . . . . . . .
Managing multiple Probe windows . . . . . . . . . . . . .
Printing multiple windows . . . . . . . . . . . . . . . .
Setting up waveform analysis . . . . . . . . . . . . . . . . . . .
Setting up colors . . . . . . . . . . . . . . . . . . . . . . . .
Editing display and print colors in the PSPICE.INI file
Configuring trace color schemes . . . . . . . . . . . . .
Viewing waveforms . . . . . . . . . . . . . . . . . . . . . . . .
Setting up waveform display from Capture . . . . . . . .
Viewing waveforms while simulating . . . . . . . . . . . .
Configuring update intervals . . . . . . . . . . . . . .
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319
320
321
322
323
323
324
324
324
326
327
327
328
329
Part four
Viewing results
Chapter 13
Analyzing waveforms
xii
319
Pspug.book Page xiii Wednesday, November 11, 1998 1:14 PM
Contents
Interacting with waveform analysis during simulation
Pausing a simulation and viewing waveforms . . . . .
Using schematic page markers to add traces . . . . . . . . .
Limiting waveform data file size . . . . . . . . . . . . . . .
Limiting file size using markers . . . . . . . . . . . . . .
Limiting file size by excluding internal subcircuit data .
Limiting file size by suppressing the first part
of simulation output . . . . . . . . . . . . . . . .
Using simulation data from multiple files . . . . . . . . . .
Appending waveform data files . . . . . . . . . . . . . .
Adding traces from specific loaded waveform data files
Saving simulation results in ASCII format . . . . . . . . . .
Analog example . . . . . . . . . . . . . . . . . . . . . . . . . . .
Running the simulation . . . . . . . . . . . . . . . . . .
Displaying voltages on nets . . . . . . . . . . . . . . . .
User interface features for waveform analysis . . . . . . . . . .
Zoom regions . . . . . . . . . . . . . . . . . . . . . . . . . .
Scrolling traces . . . . . . . . . . . . . . . . . . . . . . . . . .
Modifying trace expressions and labels . . . . . . . . . . . .
Moving and copying trace names and expressions . . . . .
Copying and moving labels . . . . . . . . . . . . . . . . . .
Tabulating trace data values . . . . . . . . . . . . . . . . . .
Using cursors . . . . . . . . . . . . . . . . . . . . . . . . . .
Displaying cursors . . . . . . . . . . . . . . . . . . . . .
Moving cursors . . . . . . . . . . . . . . . . . . . . . . .
Example: using cursors . . . . . . . . . . . . . . . . . . .
Tracking simulation messages . . . . . . . . . . . . . . . . . . .
Message tracking from the message summary . . . . . . . .
The Simulation Message Summary dialog box . . . . .
Persistent hazards . . . . . . . . . . . . . . . . . . . . . .
Message tracking from the waveform . . . . . . . . . . . . .
Trace expressions . . . . . . . . . . . . . . . . . . . . . . . . . .
Basic output variable form . . . . . . . . . . . . . . . . . . .
Output variable form for device terminals . . . . . . . . . .
Analog trace expressions . . . . . . . . . . . . . . . . . . . .
Trace expression aliases . . . . . . . . . . . . . . . . . .
Arithmetic functions . . . . . . . . . . . . . . . . . . . .
Rules for numeric values suffixes . . . . . . . . . . . . .
Chapter 14
Other output options
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329
330
331
334
334
336
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336
337
337
338
339
341
341
343
344
344
346
346
347
348
349
350
350
351
352
354
354
354
355
356
356
357
358
364
364
364
365
367
Chapter overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 367
xiii
Pspug.book Page xiv Wednesday, November 11, 1998 1:14 PM
Contents
Viewing analog results in the PSpice window . . .
Writing additional results to the PSpice output file
Generating plots of voltage and current values
Generating tables of voltage and current values
Appendix A
Setting initial state
xiv
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Convergence and “time step too small errors”
379
Appendix overview . . . . . . . . . . . . . . .
Introduction . . . . . . . . . . . . . . . . . . . .
Newton-Raphson requirements . . . . . .
Is there a solution? . . . . . . . . . . . . . .
Are the Equations Continuous? . . . . . .
Are the derivatives correct? . . . . . .
Is the initial approximation close enough?
Bias point and DC sweep . . . . . . . . . . . .
Semiconductors . . . . . . . . . . . . . . .
Switches . . . . . . . . . . . . . . . . . . . .
Behavioral modeling expressions . . . . .
Transient analysis . . . . . . . . . . . . . . . .
Skipping the bias point . . . . . . . . . . .
The dynamic range of TIME . . . . . . . .
Failure at the first time step . . . . . . . . .
Parasitic capacitances . . . . . . . . . . . .
Inductors and transformers . . . . . . . . .
Bipolar transistors substrate junction . . .
Diagnostics . . . . . . . . . . . . . . . . . . . .
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Index
395
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368
369
369
370
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373
374
374
375
376
378
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379
380
380
381
382
382
383
385
385
386
387
388
389
389
390
391
391
392
393
373
Appendix overview . .
Save and load bias point
Save bias point . . .
Load bias point . . .
Setpoints . . . . . . . . .
Setting initial conditions
Appendix B
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Pspug.book Page xv Wednesday, November 11, 1998 1:14 PM
Figures
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 11
Figure 12
Figure 13
Figure 14
Figure 15
Figure 16
Figure 17
Figure 18
Figure 19
Figure 20
Figure 21
Figure 22
Figure 23
Figure 24
Figure 25
Figure 26
Figure 27
Figure 28
Figure 29
Figure 30
Figure 31
Figure 32
Figure 33
User-configurable data files that PSpice reads . . . . . . . . . . . . . . .
Diode clipper circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Connection points. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
PSpice simulation output window. . . . . . . . . . . . . . . . . . . . . .
Simulation output file. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
DC sweep analysis settings. . . . . . . . . . . . . . . . . . . . . . . . . .
Probe window. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Clipper circuit with voltage marker on net Out. . . . . . . . . . . . . . .
Voltage at In, Mid, and Out. . . . . . . . . . . . . . . . . . . . . . . . . .
Trace legend with cursors activated. . . . . . . . . . . . . . . . . . . . .
Trace legend with V(Mid) symbol outlined. . . . . . . . . . . . . . . . .
Voltage difference at V(In) = 4 volts. . . . . . . . . . . . . . . . . . . . .
Diode clipper circuit with a voltage stimulus. . . . . . . . . . . . . . . .
Stimulus Editor window. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Transient analysis simulation settings. . . . . . . . . . . . . . . . . . . .
Sinusoidal input and clipped output waveforms. . . . . . . . . . . . . .
Clipper circuit with AC stimulus. . . . . . . . . . . . . . . . . . . . . . .
AC sweep and noise analysis simulation settings. . . . . . . . . . . . . .
dB magnitude curves for “gain” at Mid and Out. . . . . . . . . . . . . .
Bode plot of clipper’s frequency response. . . . . . . . . . . . . . . . . .
Clipper circuit with global parameter Rval. . . . . . . . . . . . . . . . .
Parametric simulation settings. . . . . . . . . . . . . . . . . . . . . . . . .
Small signal response as R1 is varied from 100Ω to 10 kΩ . . . . . . . . . .
Small signal frequency response at 100 and 10 kΩ input resistance. . .
Performance analysis plots of bandwidth and gain vs. Rval. . . . . . . .
Relationship of the Model Editor to Capture and PSpice . . . . . . . . .
Process and data flow for the Model Editor. . . . . . . . . . . . . . . . .
Model Editor workspace with data for a bipolar transistor. . . . . . . .
Design for a half-wave rectifier. . . . . . . . . . . . . . . . . . . . . . . .
Model characteristics and parameter values for DbreakX. . . . . . . . .
Assorted device characteristic curves for a diode. . . . . . . . . . . . . .
Forward Current device curve at two temperatures. . . . . . . . . . . .
. 11
. 16
. 19
. 22
. 24
. 27
. 28
. 29
. 29
. 30
. 30
. 31
. 32
. 34
. 34
. 35
. 37
. 38
. 40
. 41
. 42
. 44
. 45
. 47
. 50
. 93
. 96
. 97
104
105
108
109
Pspug.book Page xvi Wednesday, November 11, 1998 1:14 PM
Figures
Figure 34
Figure 35
Figure 36
Figure 37
Figure 38
Figure 39
Figure 40
Figure 41
Figure 42
Figure 43
Figure 44
Figure 45
Figure 46
Figure 47
Figure 48
Figure 49
Figure 50
Figure 51
Figure 52
Figure 53
Figure 54
Figure 55
Figure 56
Figure 57
Figure 58
Figure 59
Figure 60
Figure 61
Figure 62
Figure 63
Figure 64
Figure 65
Figure 66
Figure 67
Figure 68
Figure 69
Figure 70
Figure 71
Figure 72
Figure 73
Figure 74
Figure 75
xvi
Rules for pin callout in subcircuit templates. . . . . . . . . . . . . . .
LOPASS filter example. . . . . . . . . . . . . . . . . . . . . . . . . . .
HIPASS filter part example. . . . . . . . . . . . . . . . . . . . . . . . .
BANDPASS filter part example. . . . . . . . . . . . . . . . . . . . . .
BANDREJ filter part example. . . . . . . . . . . . . . . . . . . . . . .
FTABLE part example. . . . . . . . . . . . . . . . . . . . . . . . . . . .
LAPLACE part example one. . . . . . . . . . . . . . . . . . . . . . . .
Viewing gain and phase characteristics of a lossy integrator. . . . . .
LAPLACE part example two. . . . . . . . . . . . . . . . . . . . . . . .
ABM expression part example one. . . . . . . . . . . . . . . . . . . .
ABM expression part example two. . . . . . . . . . . . . . . . . . . .
ABM expression part example three. . . . . . . . . . . . . . . . . . . .
ABM expression part example four. . . . . . . . . . . . . . . . . . . .
Triode circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Triode subcircuit producing a family of I-V curves. . . . . . . . . . .
EVALUE part example. . . . . . . . . . . . . . . . . . . . . . . . . . .
GVALUE part example. . . . . . . . . . . . . . . . . . . . . . . . . . .
EMULT part example. . . . . . . . . . . . . . . . . . . . . . . . . . . .
GMULT part example. . . . . . . . . . . . . . . . . . . . . . . . . . . .
EFREQ part example. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Voltage multiplier circuit (mixer). . . . . . . . . . . . . . . . . . . . .
PSpice simulation window . . . . . . . . . . . . . . . . . . . . . . . .
Example schematic EXAMPLE.OPJ. . . . . . . . . . . . . . . . . . . .
Curve family example schematic. . . . . . . . . . . . . . . . . . . . .
Device curve family. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Operating point determination for each member of the curve family.
Circuit diagram for EXAMPLE.OPJ. . . . . . . . . . . . . . . . . . . .
AC analysis setup for EXAMPLE.OPJ. . . . . . . . . . . . . . . . . . .
Device and total noise traces for EXAMPLE.DSN. . . . . . . . . . . .
Transient analysis setup for EXAMPLE.OPJ. . . . . . . . . . . . . . .
Example schematic EXAMPLE.OPJ. . . . . . . . . . . . . . . . . . . .
ECL-compatible Schmitt trigger. . . . . . . . . . . . . . . . . . . . . .
Netlist for Schmitt trigger circuit. . . . . . . . . . . . . . . . . . . . . .
Hysteresis curve example: Schmitt trigger. . . . . . . . . . . . . . . .
Passive filter schematic. . . . . . . . . . . . . . . . . . . . . . . . . . .
Current of L1 when R1 is 1.5 ohms. . . . . . . . . . . . . . . . . . . .
Rise time and overshoot vs. damping resistance. . . . . . . . . . . . .
RLC filter example circuit. . . . . . . . . . . . . . . . . . . . . . . . . .
Plot of capacitance versus bias voltage. . . . . . . . . . . . . . . . . .
Example schematic EXAMPLE.OPJ. . . . . . . . . . . . . . . . . . . .
Example schematic EXAMPLE.DSN. . . . . . . . . . . . . . . . . . .
Monte Carlo analysis setup for EXAMPLE.DSN. . . . . . . . . . . . .
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146
157
158
159
159
162
165
165
165
169
169
170
170
171
173
177
177
178
179
185
186
210
217
221
222
222
237
238
247
263
264
266
267
268
274
276
277
278
280
282
288
290
Pspug.book Page xvii Wednesday, November 11, 1998 1:14 PM
Figures
Figure 76
Figure 77
Figure 78
Figure 79
Figure 80
Figure 81
Figure 82
Figure 83
Figure 84
Figure 85
Figure 86
Figure 87
Figure 88
Figure 89
Figure 90
Figure 91
Figure 92
Figure 93
Figure 94
Figure 95
Figure 96
Figure 97
Figure 98
Figure A-1
Summary of Monte Carlo runs for EXAMPLE.OPJ. . . . . . . . . . . .
Parameter values for Monte Carlo pass three. . . . . . . . . . . . . . .
Pressure sensor circuit. . . . . . . . . . . . . . . . . . . . . . . . . . . .
Model definition for RMonte1. . . . . . . . . . . . . . . . . . . . . . . .
Pressure sensor circuit with RMonte1 and RTherm model definitions.
Chebyshev filter. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1 dB bandwidth histogram. . . . . . . . . . . . . . . . . . . . . . . . . .
Center frequency histogram. . . . . . . . . . . . . . . . . . . . . . . . .
Simple biased BJT amplifier. . . . . . . . . . . . . . . . . . . . . . . . .
Amplifier netlist and circuit file. . . . . . . . . . . . . . . . . . . . . . .
YatX Goal Function. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Correct worst-case results. . . . . . . . . . . . . . . . . . . . . . . . . .
Incorrect worst-case results. . . . . . . . . . . . . . . . . . . . . . . . .
Schematic using VARY BOTH. . . . . . . . . . . . . . . . . . . . . . . .
Circuit file using VARY BOTH. . . . . . . . . . . . . . . . . . . . . . .
Analog and digital areas of a plot. . . . . . . . . . . . . . . . . . . . . .
Two Probe windows. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Trace legend symbols. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Section information message box. . . . . . . . . . . . . . . . . . . . . .
Example schematic EXAMPLE.OPJ. . . . . . . . . . . . . . . . . . . . .
Waveform display for EXAMPLE.DAT. . . . . . . . . . . . . . . . . .
Cursors positioned on a trough and peak of V(1) . . . . . . . . . . . .
Waveform display for a persistent hazard. . . . . . . . . . . . . . . . .
Setpoints. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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291
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321
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338
339
341
342
352
355
376
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Figures
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Tables
Table 1
Table 2
Table 3
Table 4
Table 5
Table 2-1
Table 10
Table 2-1
Table 2-1
Table 2-2
Table 2-3
Table 2-4
Table 5
Table 6
Table 7
Table 8
Table 9
Table 10
Table 11
Table 12
Table 13
Table 14
Table 15
Table 16
Table 17
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
DC analysis types . . . . . . . . . . . . . . .
AC analysis types . . . . . . . . . . . . . . .
Time-based analysis types . . . . . . . . . .
Parametric and temperature analysis types .
Statistical analysis types . . . . . . . . . . . .
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Association of cursors with mouse buttons. . . . . . . . . . . . . . . . .
Passive parts . . . . . . . . . . . . .
Breakout parts . . . . . . . . . . . .
Operators in expressions . . . . . .
Functions in arithmetic expressions
System variables . . . . . . . . . . .
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Models supported in the Model Editor . . . . . . . . . . . . . . . . . .
Sample diode data sheet values . . . . . . . . . . . . . . . . . . . . . . .
Part names for custom part generation. . . . . . . . . . . . . . . . . . . .
Control system parts . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
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3
4
5
6
7
25
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31
36
41
48
51
58
59
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. 70
. 71
. 73
74
75
77
78
80
. 95
106
133
139
141
142
145
153
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Tables
Table 1
Table 2
Table 1
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
Table 8
Table 9
Table 10
Table 11
Table 12
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 7
Table 8
Table 9
Table 10
Table 1
Table 1
Table 1
Table 2
Table 3
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
Table 1
Table 2
Table 3
Table 4
Table 5
Table 6
xx
ABM math function parts . . . . . . . . . . . . . . . .
ABM expression parts . . . . . . . . . . . . . . . . . .
PSpice -equivalent parts . . . . . . . . . . . . . . . .
Basic controlled sources in ANALOG.OLB . . . . . .
Classes of PSpice analyses . . . . . . . . . . . . . . .
Execution order for standard analyses . . . . . . . . .
PSpice output variable formats . . . . . . . . . . . .
Element definitions for 2-terminal devices . . . . . .
Element definitions for 3- or 4-terminal devices . . .
Element definitions for transmission line devices . .
Element definitions for AC analysis specific elements
DC sweep circuit design requirements . . . . . . . .
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Curve family example setup . . . . . . . . . . . . . . . . . . . . . . . . .
Stimulus symbols for time-based input signals . . . . . . . . . . . . . .
Parametric analysis circuit design requirements . . . . . . . . . . . . . .
Collating functions used in statistical analyses . . . . . . . . . . . . . . .
Default waveform viewing colors. . . . . . . . . . . . . . . . . . . . . . .
Mouse actions for cursor control . . . . . . . . . . . . . . . . . . . . . . .
Key combinations for cursor control . . . . . . . . . . . . . . . . . . . .
Output variable formats
. . . . . . . . . . . . . . . . . . . . . . . . . . .
167
168
174
192
196
198
201
202
203
204
205
214
218
218
219
221
233
233
234
234
236
242
244
246
252
272
287
294
295
300
325
326
328
330
332
333
346
351
351
357
358
358
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Tables
Table 7
Table 8
Table 9
Table 10
Table 11
Table 12
Table 13
Table 14
Table 15
Examples of output variable formats . . . . . . . .
Output variable AC suffixes . . . . . . . . . . . . .
Device names for two-terminal device types . . .
Terminal IDs by three & four-terminal device type
Noise types by device type . . . . . . . . . . . . . .
Analog arithmetic functions for trace expressions
Output units for trace expressions . . . . . . . . .
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360
361
361
362
363
364
366
369
370
xxi
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Tables
xxii
Pspug.book Page xxiii Wednesday, November 11, 1998 1:14 PM
Before you begin
Welcome to OrCAD
OrCAD® offers a total solution for your core design tasks:
schematic- and VHDL-based design entry; FPGA and
CPLD design synthesis; digital, analog, and mixed-signal
simulation; and printed circuit board layout. What's more,
OrCAD's products are a suite of applications built around
an engineer's design flow--not just a collection of
independently developed point tools. PSpice is just one
element in OrCAD's total solution design flow.
With OrCAD’s products, you’ll spend less time dealing
with the details of tool integration, devising
workarounds, and manually entering data to keep files in
sync. Our products will help you build better products
faster, and at lower cost.
Pspug.book Page xxiv Wednesday, November 11, 1998 1:14 PM
Before you begin
OrCAD PSpice overview
OrCAD PSpice simulates analog-only circuits. After you
prepare a design for simulation, OrCAD Capture
generates a circuit file set. The circuit file set, containing
the circuit netlist and analysis commands, is read by
PSpice for simulation. PSpice formulates these into
meaningful graphical plots, which you can mark for
display directly from your schematic page using markers.
xxiv
Pspug.book Page xxv Wednesday, November 11, 1998 1:14 PM
How to use this guide
How to use this guide
This guide is designed so you can quickly find the
information you need to use PSpice.
This guide assumes that you are familiar with Microsoft
Windows (NT or 95), including how to use icons, menus,
and dialog boxes. It also assumes you have a basic
understanding about how Windows manages
applications and files to perform routine tasks, such as
starting applications, and opening and saving your work.
If you are new to Windows, please review your Microsoft
Windows User’s Guide.
Typographical conventions
Before using PSpice, it is important to understand the
terms and typographical conventions used in this
documentation.
This guide generally follows the conventions used in the
Microsoft Windows User’s Guide. Procedures for
performing an operation are generally numbered with the
following typographical conventions..
Notation
Examples
Description
C+r
Press C+r
A specific key or key
stroke on the keyboard.
monospace
font
Type VAC....
Commands/text entered
from the keyborad.
xxv
Pspug.book Page xxvi Wednesday, November 11, 1998 1:14 PM
Before you begin
Related documentation
Documentation for OrCAD products is available in both
printed and online forms. To access an online manual
instantly, you can select it from the Help menu in its
respective program (for example, access the Capture
User’s Guide from the Help menu in Capture).
Note
The documentation you receive depends on the software
configuration you have purchased.
The following table provides a brief description of those
manuals available in both printed and online forms.
This manual...
Provides information about how to use...
OrCAD Capture
User’s Guide
OrCAD Capture, which is a schematic capture front-end program
with a direct interface to other OrCAD programs and options.
OrCAD Layout
User’s Guide
OrCAD Layout, which is a PCB layout editor that lets you specify
printed circuit board sturcture, as well as the components, metal,
and graphics required for fabrication.
OrCAD PSpice & Basics
User’s Guide
PSpice with Probe, the Stimulus Editor, and the Model Editor,
which are circuit analysis programs that let you create, simulate,
and test analog and digital circuit designs. This manual provides
examples on how to specify simulation parameters, analyze
simulation results, edit input signals, and create models. (PSpice
Basics is a limited version that does not include the Stimulus
Editor.)
OrCAD PSpice
User’s Guide
OrCAD PSpice with Probe is a circuit analysis program that lets
you create, simulate, and test analog-only circuit designs.
.
OrCAD PSpice Optimizer
User’s Guide
OrCAD PSpice Optimizer, which is an analog performance
optimization program that lets you fine-tune your analog circuit
designs.
The following table provides a brief description of those
manuals available online only.
xxvi
Pspug.book Page xxvii Wednesday, November 11, 1998 1:14 PM
Related documentation
This online manual...
Provides this...
OrCAD PSpice
Online Reference Manual
Reference material for PSpice. Also included: detailed descriptions of the
simulation controls and analysis specifications, start-up option
definitions, and a list of device types in the analog and digital model
libraries. User interface commands are provided to instruct you on each
of the screen commands.
OrCAD Application Notes
Online Manual
A variety of articles that show you how a particular task can be
accomplished using OrCAD’s products, and examples that demonstrate
a new or different approach to solving an engineering problem.
OrCAD PSpice Library List
A complete list of the analog and digital parts in the model and part
libraries.
Online Help
Choosing Search for Help On from the Help menu
displays an extensive online help system.
The online help includes:
•
step-by-step instructions on how to set up PSpice
simulations and analyze simulation results
•
reference information about PSpice
•
Technical Support information
If you are not familiar with Windows (NT or 95) Help
system, choose How to Use Help from the Help menu.
xxvii
Pspug.book Page xxviii Wednesday, November 11, 1998 1:14 PM
Before you begin
If you have the demo CD-ROM
OrCAD demo CD-ROM
The OrCAD demo CD-ROM has the following limitations
for PSpice:
xxviii
•
circuit simulation limited to circuits with up to 64
nodes, 10 transistors, two operational amplifiers or 65
digital primitive devices, and 10 transmission lines
(ideal or non-ideal) with not more than 4 pairwise
coupled lines
•
device characterization using the Model Editor
limited to diodes
•
stimulus generation limited to sine waves (analog)
and clocks (digital)
•
sample library of approximately 39 analog and 134
digital parts
•
displays only simulation data created using the demo
version of the simulator
•
PSpice Optimizer limited to one goal, one parameter
and one constraint
•
designs created in Capture can be saved if they have
no more than 30 part instances
Pspug.book Page xxix Wednesday, November 11, 1998 1:14 PM
What’s New
What’s New
New PSpice interface with integrated waveform
analysis functionality Release 9 of PSpice includes all
To find out more, see Analyzing
waveforms on page -319.
of Probe’s features and adds to them. Included in one
screen are tabbed windows for viewing plots, text
windows for viewing output files or other text files, and a
simulation status and message window. Also included is
a new, self-documenting analysis setup dialog for creating
simulation profiles (see below). PSpice now provides an
editable simulation queue which shows you how many
files are currently in line to be simulated. You can edit or
re-order the list as needed. And the plotting features have
been improved by providing user-controlled grid settings,
grid and trace properties (style and color) and metafile
format copy and paste functions.
Simulation profiles
PSpice Release 9 introduces the
concept of simulation profiles. Each simulation profile
refers to one schematic in a design and includes one
analysis type (AC, DC, or Transient) with any options
(sensitivity, temperature, parametric, Monte Carlo, etc.).
You can define as many profiles as you need for your
design and you can set up multiple analyses of the same
type. Simulation profiles help you keep your analysis
results separate, so you can delete one without losing the
rest.
New OrCAD Capture front-end Release 9 integrates
OrCAD Capture as the front-end schematic entry tool for
PSpice. Capture provides a professional design entry
environment with many advanced capabilities that now
work hand-in-hand with PSpice. These include a project
manager, a new property editor spreadsheet, right mouse
button support, and many other time-saving features.
xxix
Pspug.book Page xxx Wednesday, November 11, 1998 1:14 PM
Before you begin
To find out more, see Creating and
editing models on page -85.
New Model Editor interface
To find out more, refer to MOSFET devices
in the A nalog Devices chapter of the
online OrCA D PSpice A /D
Reference Manual.
EKV version 2.6 MOSFET model
The Model Editor
(formerly known as Parts) has been improved and
modernized for Release 9. It now provides a unified
application for editing models either in text form or by
modifying their specifications. The Model Editor now also
supports Darlington modeling.
The EKV model is a
scalable and compact model built on fundamental
physical properties of the device. Use this model to design
low-voltage, low-current analog, and mixed analogdigital circuits that use sub-micron technologies.
Version 2.6 models the following:
•
geometrical and process related aspects of the device
(oxide thickness, junction depth, effective channel
length and width, and so on)
•
effects of doping profile and substrate effects
•
weak, moderate, and strong inversion behavior
•
mobility effects due to vertical and lateral fields and
carrier velocity saturation
•
short-channel effects such as channel-length
modulation, source and drain charge sharing, and the
reverse short channel effect
•
thermal and flicker noise modeling
•
short-distance geometry and bias-dependent device
matching for Monte Carlo analysis
Enhanced model libraries
The model libraries
supplied with PSpice Release 9 have been enhanced to
include the latest models from various vendors, as well as
models for popular optocouplers, Darlingtons, and DAC
and ADC devices.
xxx
Pspug.book Page 31 Wednesday, November 11, 1998 1:14 PM
Part one
Simulation primer
Part one provides basic information about circuit
simulation including examples of common analyses.
•
Chapter 1, Things you need to know, provides an
overview of the circuit simulation process including
what PSpice does, descriptions of analysis types, and
descriptions of important files.
•
Chapter 2, Simulation examples, presents examples of
common analyses to introduce the methods and tools
you’ll need to enter, simulate, and analyze your
design.
Pspug.book Page 32 Wednesday, November 11, 1998 1:14 PM
Pspug.book Page 1 Wednesday, November 11, 1998 1:14 PM
Things you need to know
1
Chapter overview
This chapter introduces the purpose and function of the
OrCAD® PSpice circuit simulator.
•
What is PSpice? on page 1-2 describes PSpice
capabilities.
•
Analyses you can run with PSpice on page 1-3 introduces
the different kinds of basic and advanced analyses that
PSpice supports.
•
Using PSpice with other OrCAD programs on page 1-9
presents the high-level simulation design flow.
•
Files needed for simulation on page 1-10 describes the
files used to pass information between OrCAD
programs. This section also introduces the things you
can do to customize where and how PSpice finds
simulation information.
•
Files that PSpice generates on page 1-14 describes the
files that contain simulation results.
Pspug.book Page 2 Wednesday, November 11, 1998 1:14 PM
Chapter 1 Things you need to know
What is PSpice?
OrCAD PSpice is a simulation program that models the
behavior of a circuit containing analog devices. Used with
OrCAD Capture for design entry, you can think of PSpice
as a software-based breadboard of your circuit that you
can use to test and refine your design before ever touching
a piece of hardware.
Run basic and advanced analyses
PSpice can
perform:
The range of models built into PSpice
include not only those for resistors,
inductors, capacitors, and bipolar
transistors, but also these:
•
DC, AC, and transient analyses, so you can test the
response of your circuit to different inputs.
•
Parametric, Monte Carlo, and sensitivity/worst-case
analyses, so you can see how your circuit’s behavior
varies with changing component values.
Use parts from OrCAD’s extensive set of libraries
The model libraries feature over 11,300 analog models of
devices manufactured in North America, Japan, and
Europe.
• transmission line models, including
delay, reflection, loss, dispersion, and
crosstalk
• nonlinear magnetic core models,
including saturation and hysteresis
Vary device characteristics without creating
new parts PSpice has numerous built-in models with
parameters that you can tweak for a given device. These
include independent temperature effects.
• six MOSFET models, including BSIM3
version 3.1 and EKV version 2.6
• five GaAsFET models, including
Parker-Skellern and TriQuint’s TOM2
model
• IGBTs
2
Model behavior
PSpice supports analog behavioral
modeling, so you can describe functional blocks of
circuitry using mathematical expressions and functions.
Pspug.book Page 3 Wednesday, November 11, 1998 1:14 PM
Analyses you can run with PSpice
Analyses you can run with
PSpice
Basic analyses
See Chapter 2, Simulation
examples, for introductory examples
showing how to run each type of analysis.
See Part three, Setting Up and
Running A nalyses, for a more
detailed discussion of each type of analysis
and how to set it up.
DC sweep & other DC calculations
These DC analyses evaluate circuit performance in
response to a direct current source. Table 1 summarizes
what PSpice calculates for each DC analysis type.
Table 1
DC analysis types
For this DC analysis...
PSpice computes this...
DC sweep
Steady-state voltages and currents
when sweeping a source, a model
parameter, or temperature over a range
of values.
Bias point detail
Bias point data in addition to what is
automatically computed in any
simulation.
DC sensitivity
Sensitivity of a net or part voltage as a
function of bias point.
Small-signal
DC transfer
Small-signal DC gain, input resistance,
and output resistance as a function of
bias point.
3
Pspug.book Page 4 Wednesday, November 11, 1998 1:14 PM
Chapter 1 Things you need to know
AC sweep and noise
These AC analyses evaluate circuit performance in
response to a small-signal alternating current source.
Table 2 summarizes what PSpice calculates for each AC
analysis type.
Table 2
AC analysis types
For this AC analysis...
PSpice computes this...
AC sweep
Small-signal response of the circuit
(linearized around the bias point) when
sweeping one or more sources over a
range of frequencies. Outputs include
voltages and currents with magnitude
and phase; you can use this information
to obtain Bode plots.
Noise
For each frequency specified in the AC
analysis:
• Propagated noise contributions at an
output net from every noise
generator in the circuit.
• RMS sum of the noise contributions
at the output.
• Equivalent input noise.
Note
4
To run a noise analysis, you must also run an AC sweep analysis.
Pspug.book Page 5 Wednesday, November 11, 1998 1:14 PM
Analyses you can run with PSpice
Transient and Fourier
These time-based analyses evaluate circuit performance in
response to time-varying sources. Table 3 summarizes
what PSpice calculates for each time-based analysis type.
Table 3
Time-based analysis types
For this time-based
analysis...
PSpice computes this...
Transient
Voltages and currents tracked over
time.
Fourier
DC and Fourier components of the
transient analysis results.
Note
To run a Fourier analysis, you must also run a transient analysis.
5
Pspug.book Page 6 Wednesday, November 11, 1998 1:14 PM
Chapter 1 Things you need to know
Advanced multi-run analyses
The multi-run analyses—parametric, temperature, Monte
Carlo, and sensitivity/worst-case—result in a series of DC
sweep, AC sweep, or transient analyses depending on
which basic analyses you enabled.
Parametric and temperature
For parametric and temperature analyses, PSpice steps a
circuit value in a sequence that you specify and runs a
simulation for each value.
Table 4 shows the circuit values that you can step for each
kind of analysis.
Table 4
6
Parametric and temperature analysis types
For this analysis...
You can step one of these...
Parametric
global parameter
model parameter
component value
DC source
operational temperature
Temperature
operational temperature
Pspug.book Page 7 Wednesday, November 11, 1998 1:14 PM
Analyses you can run with PSpice
Monte Carlo and sensitivity/worst-case
Monte Carlo and sensitivity/worst-case analyses are
statistical. PSpice changes device model parameter values
with respect to device and lot tolerances that you specify,
and runs a simulation for each value.
Table 5 summarizes how PSpice runs each statistical
analysis type.
Table 5
Statistical analysis types
For this statistical
analysis...
PSpice does this...
Monte Carlo
For each simulation, randomly varies all
device model parameters for which you
have defined a tolerance.
Sensitivity/
worst-case
Computes the probable worst-case
response of the circuit in two steps:
1 Computes component sensitivity to
changes in the device model
parameters. This means PSpice
nonrandomly varies device model
parameters for which you have
defined a tolerance, one at a time for
each device and runs a simulation
with each change.
2 Sets all model parameters for all
devices to their worst-case values
(assumed to be at one of the
tolerance limits) and runs a final
simulation.
7
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Chapter 1 Things you need to know
Analyzing waveforms with
PSpice
What is waveform analysis?
Taken together, simulation and waveform
analysis is an iterative process. After
analyzing simulation results, you can refine
your design and simulation settings and
then perform a new simulation and
waveform analysis.
8
After completing the simulation, PSpice plots the
waveform results so you can visualize the circuit’s
behavior and determine the validity of your design.
Perform post-simulation analysis of the
results This means you can plot additional information
derived from the waveforms. What you can plot depends
on the types of analyses you run. Bode plots, phase
margin, derivatives for small-signal characteristics,
waveform families, and histograms are only a few of the
possibilities. You can also plot other waveform
characteristics such as rise time versus temperature, or
percent overshoot versus component value.
Pspug.book Page 9 Wednesday, November 11, 1998 1:14 PM
Using PSpice with other OrCAD programs
Using PSpice with other OrCAD
programs
Using Capture to prepare for simulation
Capture is a design entry program you need to prepare
your circuit for simulation. This means:
•
placing and connecting part symbols,
•
defining component values and other attributes,
•
defining input waveforms,
•
enabling one or more analyses, and
•
marking the points in the circuit where you want to
see results.
Capture is also the control point for running other
programs used in the simulation design flow.
What is the Stimulus Editor?
The Stimulus Editor is a graphical input waveform editor
that lets you define the shape of time-based signals used
to test your circuit’s response during simulation. Using
the Stimulus Editor, you can define:
•
analog stimuli with sine wave, pulse, piecewise linear,
exponential pulse, single-frequency FM shapes
The Stimulus Editor lets you draw analog piecewise linear
stimuli by clicking at the points along the timeline that
correspond to the input values that you want at
transitions.
9
Pspug.book Page 10 Wednesday, November 11, 1998 1:14 PM
Chapter 1 Things you need to know
What is the Model Editor?
The Model Editor is a model extractor that generates
model definitions for PSpice to use during simulation. All
the Model Editor needs is information about the device
found in standard data sheets. As you enter the data sheet
information, the Model Editor displays device
characteristic curves so you can verify the model-based
behavior of the device. When you are finished, the Model
Editor automatically creates a part for the model so you
can use the modeled part in your design immediately.
Files needed for simulation
To simulate your design, PSpice needs to know about:
•
the parts in your circuit and how they are connected,
•
what analyses to run,
•
the simulation models that correspond to the parts in
your circuit, and
•
the stimulus definitions to test with.
This information is provided in various data files. Some of
these are generated by Capture, others come from
libraries (which can also be generated by other programs
like the Stimulus Editor and the Model Editor), and still
others are user-defined.
Files that Capture generates
When you begin the simulation process, Capture first
generates files describing the parts and connections in
your circuit. These files are the netlist file and the circuit
file that PSpice reads before doing anything else.
10
Pspug.book Page 11 Wednesday, November 11, 1998 1:14 PM
Files needed for simulation
Netlist file
The netlist file contains a list of device names, values, and
how they are connected with other devices. The name that
Capture generates for this file is DESIGN_NAME.NET.
Refer to the online OrCA D PSpice
Reference Manual for the syntax of
the statements in the netlist file and the
circuit file.
Circuit file
The circuit file contains commands describing how to run
the simulation. This file also refers to other files that
contain netlist, model, stimulus, and any other
user-defined information that apply to the simulation.
The name that Capture generates for this file is
DESIGN_NAME.CIR.
Other files that you can configure for simulation
OrCAD
Stimulus Editor
global
model
libraries
OrCAD
Model Editor
model
definitions
MODEL
+ BF =
input
waveforms
stimulus file
simulation
primitives
local
model
libraries
OrCAD
PSpice
custom
include file
Figure 1 User-configurable data files that PSpice reads
Before starting simulation, PSpice needs to read other files
that contain simulation information for your circuit. These
are model files, and if required, stimulus files and include
files.
The circuit file (.CIR) that Capture generates
contains references to the other
user-configurable files that PSpice needs to
read.
11
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Chapter 1 Things you need to know
You can create these files using OrCAD programs like the
Stimulus Editor and the Model Editor. These programs
automate file generation and provide graphical ways to
verify the data. You can also use the Model Text view in
the Model Editor (or another text editor like Notepad) to
enter the data manually.
Model library
A model library is a file that contains the electrical
definition of one or more parts. PSpice uses this
information to determine how a part will respond to
different electrical inputs.
These definitions take the form of either a:
A subcircuit, sometimes called a
macromodel, is analogous to a
procedure call in a software programming
language.
•
model parameter set, which defines the behavior of a
part by fine-tuning the underlying model built into
PSpice, or
•
subcircuit netlist, which describes the structure and
function of the part by interconnecting other parts and
primitives.
The most commonly used models are available in the
OrCAD model libraries shipped with your programs. The
model library names have a .LIB extension.
If needed, however, you can create your own models and
libraries, either:
See What is the Model Editor?
on page 1-10 for a description.
12
•
manually using the Model Text view in the Model
Editor (or another text editor like Notepad), or
•
automatically using the Model Editor.
Pspug.book Page 13 Wednesday, November 11, 1998 1:14 PM
Files needed for simulation
Stimulus file
A stimulus file contains time-based definitions for analog
input waveforms. You can create a stimulus file either:
•
manually using the Model Text View of the Model
Editor (or a standard text editor) to create the
definition (a typical file extension is .STM), or
•
automatically using the Stimulus Editor (which
generates a .STL file extension).
Note Not all stimulus definitions require a
stimulus file. In some cases, like DC and AC
sources, you must use a schematic symbol
and set its attributes.
See What is the Stimulus Editor?
on page 1-9 for a description.
Include file
An include file is a user-defined file that contains:
•
PSpice commands, or
•
supplemental text comments that you want to appear
in the PSpice output file (see page 1-14).
You can create an include file using any text editor, such
as Notepad. Typically, include file names have a .INC
extension.
Configuring model library, stimulus, and
include files
PSpice searches model libraries, stimulus files, and
include files for any information it needs to complete the
definition of a part or to run a simulation.
Example: An include file that contains
definitions, using the PSpice .FUNC
command, for functions that you want to
use in numeric expressions elsewhere in
your design.
More on libraries...
Configuration for model libraries is similar
to that for other libraries that Capture uses,
including part libraries. To find out more,
refer to your Capture user’s guide.
The files that PSpice searches depend on how you
configure your model libraries and other files. Much of the
configuration is set up for you automatically, however,
you can do the following yourself:
•
Add and delete files from the configuration.
•
Change the scope of a file: that is, whether the file
applies to one design only (local) or to any design
(global).
•
Change the search order.
13
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Chapter 1 Things you need to know
Files that PSpice generates
After reading the circuit file, netlist file, model libraries,
and any other required inputs, PSpice starts the
simulation. As simulation progresses, PSpice saves results
to two files—the data file and the PSpice output file.
For a description of how to display
simulation results, see Part four,
V iewing results.
For a description of the waveform analyzer
program, see What is waveform
analysis? on page 1-8.
There are two ways to add waveforms to
the display:
• From within PSpice, by specifying trace
Waveform data file
The data file contains simulation results that that can be
displayed graphically. PSpice reads this file automatically
and displays waveforms reflecting circuit response at
nets, pins, and parts that you marked in your schematic
(cross-probing). You can set up your design so PSpice
displays the results as the simulation progresses or after
the simulation completes.
After PSpice has read the data file and displays the initial
set of results, you can add more waveforms and to
perform post-simulation analysis of the data.
expressions.
• From within Capture, by cross-probing.
PSpice output file
The PSpice output file is an ASCII text file that contains:
•
the netlist representation of the circuit,
•
the PSpice command syntax for simulation commands
and options (like the enabled analyses),
•
simulation results, and
•
warning and error messages for problems
encountered during read-in or simulation.
Its content is determined by:
Example: Each instance of a VPRINT1
symbol placed in your schematic causes
PSpice to generate a table of voltage values
for the connecting net, and to write the
table to the PSpice output file.
14
•
the types of analyses you run,
•
the options you select for running PSpice, and
•
the simulation control symbols (like VPRINT1 and
VPLOT1) that you place and connect to nets in your
design.
Pspug.book Page 15 Wednesday, November 11, 1998 1:14 PM
Simulation examples
2
Chapter overview
The examples in this chapter provide an introduction to
the methods and tools for creating circuit designs,
running simulations, and analyzing simulation results.
All analyses are performed on the same example circuit to
clearly illustrate analysis setup, simulation, and
result-analysis procedures for each analysis type.
This chapter includes the following sections:
•
Example circuit creation on page 2-16
•
Performing a bias point analysis on page 2-22
•
DC sweep analysis on page 2-26
•
Transient analysis on page 2-32
•
AC sweep analysis on page 2-37
•
Parametric analysis on page 2-42
•
Performance analysis on page 2-49
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Chapter 2 Simulation examples
Example circuit creation
This section describes how to use OrCAD Capture to
create the simple diode clipper circuit shown in Figure 2.
Figure 2 Diode clipper circuit.
To create a new PSpice project
1
From the Windows Start menu, choose the OrCAD
Release 9 program folder and then the Capture
shortcut to start Capture.
2
In the Project Manager, from the File menu, point to
New and choose Project.
3
Select Analog Circuit Wizard.
4
In the Name text box, enter the name of the project
(CLIPPER).
5
Click OK, then click Finish.
No special libraries need to be configured at this time.
A new page will be displayed in Capture and the new
project will be configured in the Project Manager.
To place the voltage sources
1
16
In Capture, switch to the schematic page editor.
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Example circuit creation
2
From the Place menu, choose Part to display the Place
Part dialog box.
3
Add the library for the parts you need to place:
a
Click the Add Library button.
b
Select SOURCE.OLB (from the PSpice library) and
click Open.
4
In the Part text box, type VDC.
5
Click OK.
6
Move the pointer to the correct position on the
schematic page (see Figure 2) and click to place the
first part.
7
Move the cursor and click again to place the second
part.
8
Right-click and choose End Mode to stop placing
parts.
or
Note There are two sets of library files
supplied with Capture and PSpice. The
standard schematic part libraries are found
in the directory Capture\Library. The part
libraries that are designed for simulation
with PSpice are found in the sub-directory
Capture\Library\PSpice. In order to have
access to specific parts, you must first
configure the library in Capture using the
Add Library function.
To place the diodes
1
From the Place menu, choose Part to display the Place
Part dialog box.
2
Add the library for the parts you need to place:
a
Click the Add Library button.
b
Select DIODE.OLB (from the PSpice library) and
click Open.
3
In the Part text box, type D1N39 to display a list of
diodes.
4
Select D1N3940 and click OK.
5
Press r to rotate the diode to the correct orientation.
6
Click to place the first diode (D1), then click to place
the second diode (D2).
7
Right-click and choose End Mode to stop placing
parts.
or
When placing parts:
• Leave space to connect the parts with
wires.
• You will change part names and values
that do not match those shown in
Figure 2 later in this section.
17
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Chapter 2 Simulation examples
To move the text associated with the diodes (or any other object)
1
Click the text to select it, then drag the text to a new
location.
To place the other parts
pre
1
From the Place menu, choose Part to display the Place
Part dialog box.
2
Add the library for the parts you need to place:
3
Click the Add Library button.
b
Select ANALOG.OLB (from the PSpice library)
and click Open.
Follow similar steps as described for the diodes to
place the parts listed below, according to Figure 2. The
part names you need to type in the Part name text box
of the Place Part dialog box are shown in parentheses:
•
resistors (R)
•
capacitor (C)
4
To place the off-page connector parts
(OFFPAGELEFT-R), click the Place Off-Page
Connector button on the tool palette.
5
Add the library for the parts you need to place:
a
Click the Add Library button.
b
Select CAPSYM.OLB (from the Capture library)
and click Open.
6
Place the off-page connector parts according to
Figure 2.
7
To place the ground parts (0), click the GND button on
the tool palette.
8
Add the library for the parts you need to place:
9
18
a
a
Click the Add Library button.
b
Select SOURCE.OLB (from the PSpice library) and
click Open.
Place the ground parts according to Figure 2.
Pspug.book Page 19 Wednesday, November 11, 1998 1:14 PM
Example circuit creation
To connect the parts
1
From the Place menu, choose Wire to begin wiring
parts.
The pointer changes to a crosshair.
2
Click the connection point (the very end) of the pin on
the off-page connector at the input of the circuit.
3
Click the nearest connection point of the input resistor
R1.
4
Connect the other end of R1 to the output capacitor.
5
Connect the diodes to each other and to the wire
between them:
a
6
Click the connection point of the cathode for the
lower diode.
b
Move the cursor straight up and click the wire
between the diodes. The wire ends, and the
junction of the wire segments becomes visible.
c
Click again on the junction to continue wiring.
d
Click the end of the upper diode’s anode pin.
or
To stop wiring, right-click and choose End
Wire. The pointer changes to the default
arrow.
Clicking on any valid connection point ends
a wire. A valid connection point is shown as
a box (see Figure 3).
Figure 3 Connection points.
If you make a mistake when placing or
connecting components:
1 From the Edit menu, choose Undo, or
click
.
Continue connecting parts until the circuit is wired as
shown in Figure 2 on page 2-16.
To assign names (labels) to the nets
1
From the Place menu, choose Net Alias to display the
Place Net Alias dialog box.
2
In the Name text box, type Mid.
3
Click OK.
4
Place the net alias on any segment of the wire that
connects R1, R2, R3, the diodes, and the capacitor. The
lower left corner of the net alias must touch the wire.
5
Right-click and choose End Mode to quit the Net Alias
function.
19
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Chapter 2 Simulation examples
To assign names (labels) to the off-page connectors
Label the off-page connectors as shown in Figure 2 on
page 2-16.
1
Double-click the name of an off-page connector to
display the Display Properties dialog box.
2
In the Name text box, type the new name.
3
Click OK.
4
Select and relocate the new name as desired.
To assign names to the parts
A more efficient way to change the
names, values and other properties of
several parts in your design is to use the
Property Editor, as follows:
1 Select all of the parts to be modified
by pressing C and clicking each
part.
2 From the Edit menu, choose
Properties.
The Parts Spreadsheet appears.
Change the entries in as many of the
cells as needed, and then click Apply to
update all of the changes at once.
1
Double-click the second VDC part to display the Parts
spreadsheet.
2
Click in the first cell under the Reference column.
3
Type in the new name Vin.
4
Click Apply to update the changes to the part, then
close the spreadsheet.
5
Continue naming the remaining parts until your
schematic looks like Figure 2 on page 2-16.
To change the values of the parts
1
Double-click the voltage label (0V) on V1 to display
the Display Properties dialog box.
2
In the Value text box, type 5V.
3
Click OK.
4
Continue changing the Part Value properties of the
parts until all the parts are defined as in Figure 2 on
page 2-16.
Your schematic page should now have the same parts,
wiring, labels, and properties as Figure 2 on page 2-16.
To save your design
pre
20
1
From the File menu, choose Save.
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Example circuit creation
Finding out more about setting up your design
About setting up a design for simulation
For a checklist of all of the things you need to do to set up
your design for simulation, and how to avoid common
problems, see Chapter 3, Preparing a design for simulation.
21
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Chapter 2 Simulation examples
Running PSpice
When you perform a simulation, PSpice generates an
output file (*.OUT).
You can set up a simulation profile to run
one analysis at a time. To run multiple
analyses (for example, both DC sweep and
transient analyses), set up a batch
simulation. For more information, see
Chapter 7, Setting up analyses
and starting simulation.
While PSpice is running, the progress of the simulation
appears and is updated in the PSpice simulation output
window (see Figure 4).
Figure 4 PSpice simulation output window.
Performing a bias point analysis
To set up a bias point analysis in Capture
The root schematic listed is the schematic
page associated with the simulation profile
you are creating.
22
1
In Capture, switch to CLIPPER.OPJ in the schematic
page editor.
2
From the PSpice menu, choose New Simulation
Profile to display the New Simulation dialog box.
3
In the Name text box, type Bias.
4
From the Inherit From list, select None, then click
Create.
The Simulation Settings dialog box appears.
5
From the Analysis type list, select Bias Point.
6
Click OK to close the Simulation Settings dialog box.
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Running PSpice
To simulate the circuit from within Capture
1
From the PSpice menu, choose Run.
PSpice simulates the circuit and calculates the bias
point information.
Note
Because waveform data is not calculated during a bias point
analysis, you will not see any plots displayed in the Probe window
for this simulation. To find out how to view the results of this
simulation, see Using the simulation output file below.
23
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Chapter 2 Simulation examples
Using the simulation output file
The simulation output file acts as an audit trail of the
simulation. This file optionally echoes the contents of the
circuit file as well as the results of the bias point
calculation. If there are any syntax errors in the netlist
declarations or simulation commands, or anomalies while
performing the calculation, PSpice writes error or
warning messages to the output file.
To view the simulation output file
1
From PSpice’s View menu, choose Output File.
Figure 5 shows the results of the bias point calculation
as written in the simulation output file.
Figure 5 Simulation output file.
2
24
When finished, close the window.
Pspug.book Page 25 Wednesday, November 11, 1998 1:14 PM
Running PSpice
PSpice measures the current through a two terminal
device into the first terminal and out of the second
terminal. For voltage sources, current is measured from
the positive terminal to the negative terminal; this is
opposite to the positive current flow convention and
results in a negative value in the output file.
Finding out more about bias point calculations
Table 2-1
To find out more about this...
See this...
bias point calculations
Bias point on page 8-223
25
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Chapter 2 Simulation examples
DC sweep analysis
You can visually verify the DC response of the clipper by
performing a DC sweep of the input voltage source and
displaying the waveform results in the Probe window in
PSpice. This example sets up DC sweep analysis
parameters to sweep Vin from -10 to 15 volts in 1 volt
increments.
Setting up and running a DC sweep analysis
To set up and run a DC sweep analysis
1
In Capture, from the PSpice menu, choose
New Simulation Profile.
The New Simulation dialog box appears.
2
In the Name text box, type DC Sweep.
3
From the Inherit From list, select Schematic1-Bias,
then click Create.
The Simulation Settings dialog box appears.
Note The default settings for DC Sweep
simulation are Voltage Source as the swept
variable type and Linear as the sweep type.
To use a different swept variable type or
sweep type, choose different options under
Sweep variable and Sweep type.
26
4
Click the Analysis tab.
5
From the Analysis type list, select DC Sweep and enter
the values shown in Figure 6.
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DC sweep analysis
Figure 6 DC sweep analysis settings.
6
Click OK to close the Simulation Settings dialog box.
7
From the File menu, choose Save.
8
From the PSpice menu, choose Run to run the analysis.
27
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Chapter 2 Simulation examples
Displaying DC analysis results
Probe windows can appear during or after the simulation
is finished.
Figure 7 Probe window.
To plot voltages at nets In and Mid
press I
1
From PSpice’s Trace menu, choose Add Trace.
2
In the Add Traces dialog box, select V(In) and V(Mid).
3
Click OK.
To display a trace using a marker
press C+M
28
1
From Capture’s PSpice menu, point to Markers and
choose Voltage Level.
2
Click to place a marker on net Out, as shown in
Figure 8.
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DC sweep analysis
Figure 8 Clipper circuit with voltage marker on net Out.
3
Right-click and choose End Mode to stop placing
markers.
4
From the File menu, choose Save.
5
Switch to PSpice. The V(Out) waveform trace appears,
as shown in Figure 9.
or
Figure 9 Voltage at In, Mid, and Out.
29
Pspug.book Page 30 Wednesday, November 11, 1998 1:14 PM
Chapter 2 Simulation examples
This example uses the cursors feature to
view the numeric values for two traces and
the difference between them by placing a
cursor on each trace.
To place cursors on V(In) and V(Mid)
1
From PSpice’s Trace menu, point to Cursor and
choose Display.
Two cursors appear for the first trace defined in the
legend below the x-axis—V(In) in this example. The
Probe Cursor window also appears.
Table 10 Association of cursors with mouse
buttons.
cursor 1
left mouse button
cursor 2
right mouse button
Figure 11 Trace legend with cursors
activated.
2
To display the cursor crosshairs:
a
Position the mouse anywhere inside the Probe
window.
b
Click to display the crosshairs for the first cursor.
c
Right-click to display the crosshairs for the second
cursor.
In the trace legend, the part for V(In) is outlined in the
crosshair pattern for each cursor, resulting in a dashed
line as shown in Figure 11.
3
Your ability to get as close to 4.0 as possible
depends on screen resolution and window
size.
4
Place the first cursor on the V(In) waveform:
a
Click the portion of the V(In) trace in the proximity
of 4 volts on the x-axis. The cursor crosshair
appears, and the current X and Y values for the
first cursor appear in the cursor window.
b
To fine-tune the cursor location to 4 volts on the
x-axis, drag the crosshairs until the x-axis value of
the A1 cursor in the cursor window is
approximately 4.0. You can also press r and l
for tighter control.
Place the second cursor on the V(Mid) waveform:
a
Right-click the trace legend part (diamond) for
V(Mid) to associate the second cursor with the Mid
waveform. The crosshair pattern for the second
cursor outlines the V(Mid) trace part as shown in
Figure 12.
b
Right-click the portion on the V(Mid) trace that is
in the proximity of 4 volts on the x-axis. The X and
Y values for the second cursor appear in the cursor
window along with the difference (dif) between
the two cursors’ X and Y values.
Figure 12 Trace legend with V(Mid)
symbol outlined.
30
Pspug.book Page 31 Wednesday, November 11, 1998 1:14 PM
DC sweep analysis
c
To fine-tune the location of the second cursor to 4
volts on the x-axis, drag the crosshairs until the
x-axis value of the A2 cursor in the cursor window
is approximately 4.0. You can also press V+r
and V+l for tighter control.
Figure 13 shows the Probe window with both cursors
placed.
There are also ways to display the
difference between two voltages as a trace:
• In PSpice, add the trace expression
V(In)-V(Mid).
• In Capture, from the PSpice menu,
point to Markers and choose Voltage
Differential. Place the two markers on
different pins or wires.
Figure 13 Voltage difference at V(In) = 4 volts.
To delete all of the traces
1
From the Trace menu, choose Delete All Traces.
At this point, the design has been saved. If needed,
you can quit Capture and PSpice and complete the
remaining analysis exercises later using the saved
design.
You can also delete an individual trace by
selecting its name in the trace legend and
then pressing D.
Example: To delete the V(In) trace, click the
text, V(In), located under the plot’s
x-axis, and then press D.
Finding out more about DC sweep analysis
Table 2-1
To find out more about this...
See this...
DC sweep analysis
DC Sweep on page 8-214
31
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Chapter 2 Simulation examples
Transient analysis
This example shows how to run a transient analysis on the
clipper circuit. This requires adding a time-domain
voltage stimulus as shown in Figure 14.
Figure 14 Diode clipper circuit with a voltage stimulus.
32
Pspug.book Page 33 Wednesday, November 11, 1998 1:14 PM
Transient analysis
To add a time-domain voltage stimulus
1
From Capture’s PSpice menu, point to Markers and
choose Delete All.
2
Select the ground part beneath the VIN source.
3
From the Edit menu, choose Cut.
4
Scroll down (or from the View menu, point to Zoom,
then choose Out).
5
Place a VSTIM part (from the PSpice library
SOURCESTM.OLB) as shown in Figure 14.
6
From the Edit menu, choose Paste.
7
Place the ground part under the VSTIM part as shown
in Figure 14.
8
From the View menu, point to Zoom, then choose All.
9
From the File menu, choose Save to save the design.
or press C+v
To set up the stimulus
1
Select the VSTIM part (V3).
2
From the Edit menu, choose PSpice Stimulus.
The New Stimulus dialog box appears.
3
In the New Stimulus dialog box, type SINE.
4
Click SIN (sinusoidal), then click OK.
5
In the SIN Attributes dialog box, set the first three
properties as follows:
Offset Voltage = 0
Amplitude = 10
Frequency = 1kHz
6
Note The Stimulus Editor is
not included in PSpice Basics.
If you do not have the
Stimulus Editor
1 Place a VSIN part instead of VSTIM and
double-click it.
2 In the Edit Part dialog box, click User
Properties.
3 Set values for the VOFF, VAMPL, and
FREQ properties as defined in step 5.
When finished, click OK.
Click Apply to view the waveform.
The Stimulus Editor window should look like
Figure 15.
33
Pspug.book Page 34 Wednesday, November 11, 1998 1:14 PM
Chapter 2 Simulation examples
Figure 15 Stimulus Editor window.
press [email protected]
7
Click OK.
8
From the File menu, choose Save to save the stimulus
information. Click Yes to update the schematic.
9
From the File menu, choose Exit to exit the Stimulus
Editor.
To set up and run the transient analysis
1
From Capture’s PSpice menu, choose
New Simulation Profile.
The New Simulation dialog box appears.
2
In the Name text box, type Transient.
3
From the Inherit From list, select
Schematic1-DC Sweep, then click Create.
The Simulation Settings dialog box appears.
4
Click the Analysis tab.
5
From the Analysis list, select Time Domain (Transient)
and enter the settings shown in Figure 16.
TSTOP = 2ms
Figure 16 Transient analysis simulation
settings.
34
Start saving data after = 20ns
Pspug.book Page 35 Wednesday, November 11, 1998 1:14 PM
Transient analysis
6
Click OK to close the Simulation Settings dialog box.
7
From the PSpice menu, choose Run to perform the
analysis.
PSpice uses its own internal time steps for
computation. The internal time step is adjusted
according to the requirements of the transient analysis
as it proceeds. PSpice saves data to the waveform data
file for each internal time step.
Note The internal time step is different
from the Print Step value. Print Step
controls how often optional text format
data is written to the simulation output
file (*.OUT).
To display the input sine wave and clipped wave at V(Out)
1
From PSpice’s Trace menu, choose Add Trace.
2
In the trace list, select V(In) and V(Out) by clicking
them.
3
Click OK to display the traces.
4
From the Tools menu, choose Options to display the
Probe Options dialog box.
5
In the Use Symbols frame, click Always if it is not
already enabled.
6
Click OK.
or press I
These waveforms illustrate the clipping of
the input signal.
Figure 17 Sinusoidal input and clipped output waveforms.
35
Pspug.book Page 36 Wednesday, November 11, 1998 1:14 PM
Chapter 2 Simulation examples
Finding out more about transient analysis
Table 2-1
To find out more about this...
See this...
transient analysis for analog
designs*
Chapter 10, Transient
analysis
* Includes how to set up time-based stimuli using the Stimulus Editor.
36
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AC sweep analysis
AC sweep analysis
The AC sweep analysis in PSpice is a linear (or small
signal) frequency domain analysis that can be used to
observe the frequency response of any circuit at its bias
point.
Setting up and running an AC sweep analysis
In this example, you will set up the clipper circuit for AC
analysis by adding an AC voltage source for a stimulus
signal (see Figure 18) and by setting up AC sweep
parameters.
Figure 18 Clipper circuit with AC stimulus.
To change Vin to include the AC stimulus signal
1
In Capture, open CLIPPER.OPJ.
2
Select the DC voltage source, Vin, and press D to
remove the part from the schematic page.
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Chapter 2 Simulation examples
3
From the Place menu, choose Part.
4
In the Part text box, type VAC (from the PSpice library
SOURCE.OLB) and click OK.
5
Place the AC voltage source on the schematic page, as
shown in Figure 17.
6
Double-click the VAC part (0V) to display the Parts
spreadsheet.
7
Change the Reference cell to Vin and change the
ACMAG cell to 1V.
8
Click Apply to update the changes and then close the
spreadsheet.
To set up and run the AC sweep simulation
Note PSpice simulation is not
case-sensitive, so both M and m can be used
as “milli,” and MEG, Meg, and meg can all
be used for “mega.” However, waveform
analysis treats M and m as mega and milli,
respectively.
1
From Capture’s PSpice menu, choose New Simulation
Profile.
2
In the Name text box, enter AC Sweep, then click
create.
The Simulation Settings dialog box appears.
3
Click the Analysis tab.
4
From the Analysis type list, select AC Sweep/Noise
and enter the settings shown in Figure 19.
Figure 19 AC sweep and noise analysis simulation settings.
38
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AC sweep analysis
5
Click OK to close the Simulation Settings dialog box.
6
From the PSpice menu, choose Run to start the
simulation.
PSpice performs the AC analysis.
To add markers for waveform analysis
1
From Capture’s PSpice menu, point to Markers, point
to Advanced, then choose db Magnitude of Voltage.
2
Place one Vdb marker on the Out net, then place
another on the Mid net.
3
From the File menu, choose Save to save the design.
Note You must first define a simulation
profile for the AC Sweep/Noise analysis
in order to use advanced markers.
AC sweep analysis results
PSpice displays the dB magnitude (20log10) of the voltage
at the marked nets, Out and Mid, in a Probe window as
shown in Figure 20 below. VDB(Mid) has a lowpass
response due to the diode capacitances to ground. The
output capacitance and load resistor act as a highpass
filter, so the overall response, illustrated by VDB(out), is a
bandpass response. Because AC is a linear analysis and
the input voltage was set to 1V, the output voltage is the
same as the gain (or attenuation) of the circuit.
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Chapter 2 Simulation examples
Figure 20 dB magnitude curves for “gain” at Mid and Out.
To display a Bode plot of the output voltage, including phase
Note Depending upon where the Vphase
marker was placed, the trace name may be
different, such as VP(Cout:2), VP(R4:1), or
VP(R4:2).
For more information on Probe windows
and trace expressions, see Chapter 13,
Analyzing waveforms.
press C+x
press C+V
1
From Capture’s PSpice menu, point to Markers, point
to Advanced and choose Phase of Voltage.
2
Place a Vphase marker on the output next to the Vdb
marker.
3
Delete the Vdb marker on Mid.
4
Switch to PSpice.
In the Probe window, the gain and phase plots both
appear on the same graph with the same scale.
5
Click the trace name VP(Out) to select the trace.
6
From the Edit menu, choose Cut.
7
From the Plot menu, choose Add Y Axis.
8
From the Edit menu, choose Paste.
The Bode plot appears, as shown in Figure 21.
40
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AC sweep analysis
Figure 21 Bode plot of clipper’s frequency response.
Finding out more about AC sweep and
noise analysis
Table 2-2
To find out more about this...
See this...
AC sweep analysis
AC sweep analysis on
page 9-232
noise analysis based on an
AC sweep analysis
Noise analysis on
page 9-241
41
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Chapter 2 Simulation examples
Parametric analysis
Note Parametric Analysis is
not supported in PSpice
Basics.
This example shows the effect of varying input resistance
on the bandwidth and gain of the clipper circuit by:
•
Changing the value of R1 to the expression {Rval}.
•
Placing a PARAM part to declare the parameter Rval.
•
Setting up and running a parametric analysis to step
the value of R1 using Rval.
Figure 22 Clipper circuit with global parameter Rval.
This example produces multiple analysis runs, each with
a different value of R1. After the analysis is complete, you
can analyze curve families for the analysis runs using
PSpice.
42
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Parametric analysis
Setting up and running the parametric analysis
To change the value of R1 to the expression {Rval}
1
In Capture, open CLIPPER.OPJ.
2
Double-click the value (1k) of part R1 to display the
Display Properties dialog box.
3
In the Value text box, replace 1k with {Rval}.
4
Click OK.
PSpice interprets text in curly braces as an
expression that evaluates to a numerical
value. This example uses the simplest form
of an expression—a constant. The value of
R1 will take on the value of the Rval
parameter, whatever it may be.
To add a PARAM part to declare the parameter Rval
1
From Capture’s Place menu, choose Part.
2
In the Part text box, type PARAM (from the PSpice
library SPECIAL.OLB) , then click OK.
3
Place one PARAM part in any open area on the
schematic page.
4
Double-click the PARAM part to display the Parts
spreadsheet, then click New.
5
In the Property Name text box, enter Rval (no curly
braces), then click OK.
Note For more information about using
the Parts spreadsheet, see the OrCAD
Capture User’s Guide.
This creates a new property for the PARAM part, as
shown by the new column labeled Rval in the
spreadsheet.
6
Click in the cell below the Rval column and enter 1k
as the initial value of the parametric sweep.
7
While this cell is still selected, click Display.
8
In the Display Format frame, select Name and Value,
then click OK.
9
Click Apply to update all the changes to the PARAM
part.
10 Close the Parts spreadsheet.
11 Select the VP marker and press D to remove the
marker from the schematic page.
This example is only interested in the
magnitude of the response.
12 From the File menu, choose Save to save the design.
43
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Chapter 2 Simulation examples
To set up and run a parametric analysis to step the value of R1
using Rval
1
From Capture’s PSpice menu, choose
New Simulation Profile.
The New Simulation dialog box appears.
The root schematic listed is the schematic
page associated with the simulation profile
you are creating.
2
In the Name text box, type Parametric.
3
From the Inherit From list, select AC Sweep, then click
Create.
The Simulation Settings dialog box appears.
4
Click the Analysis tab.
5
Under Options, select Parametric Sweep and enter the
settings as shown below.
This profile specifies that the parameter
Rval is to be stepped from 100 to 10k
logarithmically with a resolution of 10
points per decade.
The analysis is run for each value of Rval.
Because the value of R1 is defined as
{Rval}, the analysis is run for each value of
R1 as it logarithmically increases from
100Ω to 10 kΩ in 20 steps, resulting in a
total of 21 runs.
Figure 23 Parametric simulation settings.
44
6
Click OK.
7
From the PSpice menu, choose Run to start the
analysis.
Pspug.book Page 45 Wednesday, November 11, 1998 1:14 PM
Parametric analysis
Analyzing waveform families
Continuing from the example above, there are 21 analysis
runs, each with a different value of R1. After PSpice
completes the simulation, the Available Sections dialog
box appears, listing all 21 runs and the Rval parameter
value for each. You can select one or more runs to display.
To display all 21 traces
1
In the Available Sections dialog box, click OK.
All 21 traces (the entire family of curves) for VDB(Out)
appear in the Probe window as shown in Figure 24.
To select individual runs, click each one
separately.
To see more information about the section
that produced a specific trace, double-click
the corresponding symbol in the legend
below the x-axis.
Figure 24 Small signal response as R1 is varied from 100Ω
to 10 kΩ
2
Click the trace name to select it, then press D to
remove the traces shown.
You can also remove the traces by
removing the VDB marker from your
schematic page in Capture.
45
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Chapter 2 Simulation examples
To compare the last run to the first run
press I
You can avoid some of the typing for the
Trace Expression text box by selecting
V(OUT) twice in the trace list and inserting
text where appropriate in the resulting
Trace Expression.
1
From the Trace menu, choose Add Trace to display the
Add Traces dialog box.
2
In the Trace Expression text box, type the following:
Vdb(Out)@1 Vdb(Out)@21
3
Click OK.
The difference in gain is apparent. You can also plot the difference
of the waveforms for runs 21 and 1, then use the search commands
to find certain characteristics of the difference.
Note
4
press I
Plot the new trace by specifying a waveform
expression:
a
From the Trace menu, choose Add Trace.
b
In the Trace Expression text box, type the
following waveform expression:
Vdb(Out)@1-Vdb(OUT)@21
c
5
The search command tells PSpice to search
for the point on the trace where the x-axis
value is 100.
46
Click OK.
Use the search commands to find the value of the
difference trace at its maximum and at a specific
frequency:
a
From the Tools menu, point to Cursor and choose
Display.
b
Right-click then left-click the trace part (triangle)
for Vdb(Out)@1 - Vdb(Out)@21. Make sure that
you left-click last to make cursor 1 the active
cursor.
c
From the Trace menu, point to Cursor and choose
Max.
d
From the Trace menu, point to Cursor and choose
Search Commands.
e
In the Search Command text box, type the
following:
search forward x value (100)
f
Select 2 as the Cursor to Move option.
Pspug.book Page 47 Wednesday, November 11, 1998 1:14 PM
Parametric analysis
g
Click OK.
Figure 25 shows the Probe window with cursors
placed.
Figure 25 Small signal frequency response at 100 and 10 kΩ
input resistance.
Note that the Y value for cursor 2 in the cursor box is
about 17.87. This indicates that when R1 is set to 10 kΩ,
the small signal attenuation of the circuit at 100Hz is
17.87dB greater than when R1 is 100Ω.
6
From the Trace menu, point to Cursor and choose
Display to turn off the display of the cursors.
7
Delete the trace.
47
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Chapter 2 Simulation examples
Finding out more about parametric analysis
Table 2-3
48
To find out more about this...
See this...
parametric analysis
Parametric analysis on
page 11-272
using global parameters
Using global parameters and
expressions for values on
page 3-67
Pspug.book Page 49 Wednesday, November 11, 1998 1:14 PM
Performance analysis
Performance analysis
Performance analysis is an advanced feature in PSpice
that you can use to compare the characteristics of a family
of waveforms. Performance analysis uses the principle of
search commands introduced earlier in this chapter to
define functions that detect points on each curve in the
family.
After you define these functions, you can apply them to a
family of waveforms and produce traces that are a
function of the variable that changed within the family.
This example shows how to use performance analysis to
view the dependence of circuit characteristics on a swept
parameter. In this case, the small signal bandwidth and
gain of the clipper circuit are plotted against the swept
input resistance value.
To plot bandwidth vs. Rval using the performance analysis wizard
1
In Capture, open CLIPPER.OPJ.
2
From PSpice’s Trace menu, choose Performance
Analysis.
The Performance Analysis dialog box appears with
information about the currently loaded data and
performance analysis in general.
3
Click the Wizard button.
4
Click the Next> button.
5
In the Choose a Goal Function list, click Bandwidth,
then click the Next> button.
6
Click in the Name of Trace to search text box and type
V(Out).
7
Click in the db level down for bandwidth calc text box
and type 3.
8
Click the Next> button.
At each step, the wizard provides
information and guidelines.
Click
, then double-click V(Out).
The wizard displays the gain trace for the first run
(R=100) and shows how the bandwidth is measured.
This is done to test the goal function.
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Chapter 2 Simulation examples
9
Click the Next> button or the Finish button.
A plot of the 3dB bandwidth vs. Rval appears.
10 Change the x-axis to log scale:
Double-click the x-axis.
a
From the Plot menu, choose Axis Settings.
b
Click the X Axis tab.
c
Under Scale, choose Log.
d
Click OK.
To plot gain vs. Rval manually
or press I
The Trace list includes goal functions only in
performance analysis mode when the
x-axis variable is the swept parameter.
1
From the Plot menu, choose Add Y Axis.
2
From the Trace menu, choose Add to display the Add
Traces dialog box.
3
In the Functions or Macros frame, select the Goal
Functions list, and then click the Max(1) goal function.
4
In the Simulation Output Variables list, click V(out).
5
In the Trace Expression text box, edit the text to be
Max(Vdb(out)), then click OK.
PSpice displays gain on the second y-axis vs. Rval.
Figure 26 shows the final performance analysis plot of 3dB
bandwidth and gain in dB vs. the swept input resistance
value.
Figure 26 Performance analysis plots of bandwidth and gain vs.
Rval.
50
Pspug.book Page 51 Wednesday, November 11, 1998 1:14 PM
Performance analysis
Finding out more about performance analysis
Table 2-4
To find out more about this...
See this...
how to use performance
analysis
RLC filter example on
page 11-274
Example: Monte Carlo
analysis of a pressure sensor
on page 12-293
how to use search
commands and create goal
functions
PSpice A/D online Help
51
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Chapter 2 Simulation examples
52
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Part two
Design entry
Part two provides information about how to enter circuit
designs in OrCAD® Capture that you want to simulate.
•
Chapter 3, Preparing a design for simulation, outlines the
things you need to do to successfully simulate your
schematic including troubleshooting tips for the most
frequently asked questions.
•
Chapter 4, Creating and editing models, describes how to
use the tools to create and edit model definitions, and
how to configure the models for use.
•
Chapter 5, Creating parts for models, explains how to
create symbols for existing or new model definitions
so you can use the models when simulating from your
schematic.
•
Chapter 6, Analog behavioral modeling, describes how to
model analog behavior mathematically or using table
lookups.
Pspug.book Page 54 Wednesday, November 11, 1998 1:14 PM
Pspug.book Page 55 Wednesday, November 11, 1998 1:14 PM
Preparing a design for
simulation
3
Chapter overview
This chapter provides introductory information to help
you enter circuit designs that simulate properly. If you
want an overview, use the checklist on page 3-56 to guide
you to specific topics.
Topics include:
•
Checklist for simulation setup on page 3-56
•
Using parts that you can simulate on page 3-60
•
Using global parameters and expressions for values on
page 3-67
•
Defining power supplies on page 3-74
•
Defining stimuli on page 3-75
•
Things to watch for on page 3-79
Refer to your OrCA D Capture
User’s Guide for general schematic
entry information.
Pspug.book Page 56 Wednesday, November 11, 1998 1:14 PM
Chapter 3 Preparing a design for simulation
Checklist for simulation setup
This section describes what you need to do to set up your
circuit for simulation.
1
Find the topic that is of interest in the first column of
any of these tables.
2
Go to the referenced section. For those sections that
provide overviews, you will find references to more
detailed discussions.
Typical simulation setup steps
For more information on this step...
See this...
To find out this...
✔ Set component values
Using parts that you can
simulate on page 3-60
An overview of vendor, passive,
breakout, and behavioral parts.
Using global parameters and
expressions for values on
page 3-67
How to define values using variable
parameters, functional calls, and
mathematical expressions.
Defining power supplies on
page 3-74
An overview of DC power for
analog circuits..
Defining stimuli on
page 3-75
An overview of DC, AC, and
time-based stimulus parts.
Chapter 7, Setting up
analyses and starting
simulation
Procedures, general to all analysis
types, to set up and start the
simulation.
Chapter 8 through
Chapter 12 (see the table of
Detailed information about DC, AC,
transient, parametric, temperature,
Monte Carlo, and
sensitivity/worst-case..
and other properties.
✔ Define power
supplies.
✔ Define input
waveforms.
✔ Set up one or more
analyses.
contents)
56
Pspug.book Page 57 Wednesday, November 11, 1998 1:14 PM
Checklist for simulation setup
For more information on this step...
See this...
✔ Place markers.
Using schematic page
markers to add traces on
page 13-331
How to display results in PSpice by
picking design nets.
✔
Limiting waveform data file
size on page 13-334
How to limit the data file size.
Advanced design entry and simulation setup steps
For more information on this step...
See this...
To find out how to...
✔ Create new models.
Chapter 4, Creating and
editing models
Define models using the Model
Editor or Create Subcircuit
command.
Chapter 6, Analog
behavioral modeling
Define the behavior of a block of
analog circuitry as a mathematical
function or lookup table.
Chapter 5, Creating parts
for models
Create parts either automatically for
models using the part wizard or the
Parts utility, or by manually
defining AKO parts; define
simulation-specific properties.
The OrCA D Capture User’s
Create and edit part graphics, pins,
and properties in general.
✔ Create new parts.
Guide
57
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Chapter 3 Preparing a design for simulation
When netlisting fails or the simulation
does not start
If you have problems starting the simulation, there may be
problems with the design or with system resources. If
there are problems with the design, PSpice displays errors
and warnings in the Simulation Output window. You can
use the Simulation Output window to get more
information quickly about the specific problem.
To get online information about an error or warning shown in the
Simulation Output window
1
Select the error or warning message.
2
Press 1.
The following tables list the most commonly encountered
problems and where to find out more about what to do.
Things to check in your design
Table 5
Make sure that...
To find out more, see this...
✔ The model libraries, stimulus files, and
Configuring model libraries on page 4-120
include files are configured.
✔ The parts you are using have models.
Unmodeled parts on page 3-79 and Defining part
properties needed for simulation on page 5-139
✔ You are not using unmodeled pins.
Unmodeled pins on page 3-82
✔ You have defined the grounds.
Missing ground on page 3-83
✔ Every analog net has a DC path to ground. Missing DC path to ground on page 3-84
✔ The part template is correct.
Defining part properties needed for simulation on
page 5-139
✔ Hierarchical parts, if used, are properly
The OrCA D Capture User’s Guide
defined.
✔ Ports that connect to the same net have the The OrCA D Capture User’s Guide
same name.
58
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Checklist for simulation setup
Things to check in your system configuration
Table 6
Make sure that...
To find out more, see this...
✔ Path to the PSpice programs is correct.
✔ Directory containing your design has write Your operating system manual
permission.
✔ Your system has sufficient free memory
Your operating system manual
and disk space.
59
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Chapter 3 Preparing a design for simulation
Using parts that you can
simulate
The OrCAD part libraries also include
special parts that you can use for
simulation only. These include:
• stimulus parts to generate
input signals to the circuit (see
Defining stimuli on
page 3-75)
• ground parts required by all
analog circuits, which need reference
to ground
• simulation control parts
The OrCAD part libraries supply numerous parts
designed for simulation. These include:
•
vendor-supplied parts
•
passive parts
•
breakout parts
•
behavioral parts
At minimum, a part that you can simulate has these
properties:
•
to do things like set bias values (see
Appendix A, Setting initial
state)
• output control parts to do
things like generate tables and
line-printer plots to the PSpice output
file (see Chapter 14, Other
output options)
•
explicitly defined in a model library,
•
built into PSpice, or
•
built into the part (for some kinds of analog
behavioral parts).
•
A part with modeled pins to form electrical
connections in your design.
•
A translation from design part to netlist statement so
that PSpice can read it in.
Note
60
A simulation model to describe the part’s electrical
behavior; the model can be:
Not all parts in the libraries are set up for simulation. For example,
connectors are parts destined for board layout only and do not
have these simulation properties.
Pspug.book Page 61 Wednesday, November 11, 1998 1:14 PM
Using parts that you can simulate
Vendor-supplied parts
The OrCAD libraries provide an extensive selection of
manufacturers’ analog parts. Typically, the library name
reflects the kind of parts contained in the library and the
vendor that provided the models.
Example: MOTOR_RF.OLB and MOTOR_RF.LIB contain
parts and models, respectively, for Motorola-made RF
bipolar transistors.
For a listing of vendor-supplied parts
contained in the OrCAD libraries, refer to
the online Library List.
To find out more about each model library,
read the comments in the .LIB file header.
Part naming conventions
The part names in the OrCAD libraries usually reflect the
manufacturers’ part names. If multiple vendors supply
the same part, each part name includes a suffix that
indicates the vendor that supplied the model.
Example: The OrCAD libraries include several models for
the OP-27 opamp as shown by these entries in the online
Library List.
61
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Chapter 3 Preparing a design for simulation
Notice the following:
•
There is a generic OP-27 part provided by OrCAD, the
OP-27/AD from Analog Devices, Inc., and the
OP-27/LT from Linear Technology Corporation.
•
The Model column for all of these parts contains an
asterisk. This indicates that this part is modeled and
that you can simulate it.
Finding the part that you want
If you are having trouble finding a part, you can search the
libraries for parts with similar names by using either:
•
the parts browser in Capture and restricting the parts
list to those names that match a specified wildcard text
string, or
•
the online Library List and searching for the generic
part name using capabilities of the Adobe Acrobat
Reader.
To find parts using the parts browser
Note This method finds any part contained
in the current part libraries configuration,
including parts for user-defined models.
If you want to find out more about a part
supplied in the OrCAD libraries, such as
manufacturer or whether you can simulate
it, then search the online Library List
(see page 3-63).
1
In Capture, from the Place menu, choose Part.
2
In the Part Name text box, type a text string with
wildcards that approximates the part name that you
want to find. Use this syntax:
<wildcard><part_name_fragment><wildcard>
where <wildcard> is one of the following:
*
to match zero or more characters
?
to match exactly one character
The parts browser displays only the matching part
names.
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Using parts that you can simulate
To find parts using the online OrCAD Library List
1
In Windows Explorer, double-click LIBLIST.PDF,
located in the directory where PSpice is installed.
Acrobat Reader starts and displays the OrCAD
Library List.
2
From the Tools menu, choose Find.
3
In the Find What text box, type the generic part name.
4
Enter any other search criteria, and then click Find.
The Acrobat Reader displays the first page where it
finds a match. Each page maps the generic part name
to the parts (and corresponding vendor and part
library name) in the OrCAD libraries.
5
Note
If you want to repeat the search, from the Tools menu,
choose Find Again.
Note This method finds only parts that
OrCAD supplies that have models.
If you want to include user-defined parts in
the search, use the parts browser in Capture
(see page 3-62).
or press C+F
Instead of the generic part name, you can
enter other kinds of search information,
such as device type or manufacturer.
press C+G
If you are unsure of the device type, you can scan all of the device
type lists using the Acrobat search capability. The first time you do
this, you need to set up the across-list index. To find out more, refer
to the online Adobe Acrobat manuals.
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Chapter 3 Preparing a design for simulation
Passive parts
The OrCAD libraries supply several basic parts based on
the passive device models built into PSpice. These are
summarized in the following table.
Table 7
To find out more about how to use these
parts and define their properties, look up
the corresponding PSpice device letter in
the A nalog Devices chapter in the
online OrCA D PSpice A /D
Reference Manual, and then see the
Capture Parts sections.
Passive parts
These parts are
available...
For this device type...
Which is this PSpice
device letter...
C
C_VAR
capacitor
C
L
inductor
L
R
R_VAR
resistor
R
XFRM_LINEAR
K_LINEAR
transformer
K and L
T
ideal transmission line
T
TLOSSY
Lossy transmission line
T
TnCOUPLED*
TnCOUPLEDX**
KCOUPLEn**
coupled transmission line
T and K
* For these device types, the OrCAD libraries supply several parts. Refer to the
online OrCA D PSpice A /D Reference Manual for the available
parts.
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Using parts that you can simulate
Breakout parts
The OrCAD libraries supply passive and semiconductor
parts with default model definitions that define a basic set
of model parameters. This way, you can easily:
•
assign device and lot tolerances to model parameters
for Monte Carlo and sensitivity/worst-case analyses,
•
define temperature coefficients, and
•
define device-specific operating temperatures.
These are called breakout parts and are summarized in the
following table.
Table 8
Breakout parts
Use this
breakout part...
For this device type...
Which is this PSpice
device letter...
BBREAK
GaAsFET
B
CBREAK
capacitor
C
DBREAKx *
diode
D
JBREAKx *
JFET
J
KBREAK
inductor coupling
K
LBREAK
inductor
L
MBREAKx *
MOSFET
M
QBREAKx*
bipolar transistor
Q
RBREAK
resistor
R
SBREAK
voltage-controlled
switch
S
TBREAK
transmission line
T
WBREAK
current-controlled
switch
W
XFRM_NONLINEAR
transformer
K and L
ZBREAKN
IGBT
Z
To find out more about models, see What
are models? on page 4-87.
To find out more about Monte Carlo and
sensitivity/worst-case analyses, see
Chapter 12, Monte Carlo and
sensitivity/worst-case analyses.
To find out more about setting temperature
parameters, see the A nalog Devices
chapter in the online OrCA D PSpice
A /D Reference Manual and find the
device type that you are interested in.
To find out more about how to use these
parts and define their properties, look up
the corresponding PSpice device letter in
the A nalog Devices chapter of the
online OrCA D PSpice A /D
Reference Manual, and then look in
the Capture Parts section.
* For this device type, the OrCAD libraries supply several breakout parts. Refer
to the online OrCA D PSpice Reference Manual for the available
parts.
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Chapter 3 Preparing a design for simulation
Behavioral parts
Behavioral parts allow you to define how a block of
circuitry should work without having to define each
discrete component.
For more information, see Chapter 6,
Analog behavioral modeling.
66
Analog behavioral parts These parts use analog
behavioral modeling (ABM) to define each part’s behavior
as a mathematical expression or lookup table. The OrCAD
libraries provide ABM parts that operate as math
functions, limiters, Chebyshev filters, integrators,
differentiators, and others that you can customize for
specific expressions and lookup tables. You can also create
your own ABM parts.
Pspug.book Page 67 Wednesday, November 11, 1998 1:14 PM
Using global parameters and expressions for values
Using global parameters and
expressions for values
In addition to literal values, you can use global parameters
and expressions to represent numeric values in your
circuit design.
Global parameters
A global parameter is like a programming variable that
represents a numeric value by name.
Once you have defined a parameter (declared its name
and given it a value), you can use it to represent circuit
values anywhere in the design; this applies to any
hierarchical level.
Some ways that you can use parameters are as follows:
•
Apply the same value to multiple part instances.
•
Set up an analysis that sweeps a variable through a
range of values (for example, DC sweep or parametric
analysis).
When multiple parts are set to the same
value, global parameters provide a
convenient way to change all of their
values for “what-if” analyses.
Example: If two independent sources have
a value defined by the parameter
VSUPPLY, then you can change both
sources to 10 volts by assigning the value
once to VSUPPLY.
Declaring and using a global parameter
To use a global parameter in your design, you need to:
•
define the parameter using a PARAM part, and
•
use the parameter in place of a literal value
somewhere in your design.
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Chapter 3 Preparing a design for simulation
To declare a global parameter
Note For more information about using
the Parts spreadsheet, see the OrCAD
Capture User’s Guide.
1
Place a PARAM part in your design.
2
Double-click the PARAM part to display the Parts
spreadsheet, then click New.
3
Declare up to three global parameters by doing the
following for each global parameter:
Example: To declare the global parameter
VSUPPLY that will set the value of an
independent voltage source to 14 volts,
place the PARAM part, and then create a
new property named VSUPPLY with a
value of 14v.
a
Click New.
b
In the Property Name text box, enter NAMEn, then
click OK.
This creates a new property for the PARAM part,
NAMEn in the spreadsheet.
Note
c
Click in the cell below the NAMEn column and
enter a default value for the parameter.
d
While this cell is still selected, click Display.
e
In the Display Format frame, select Name and
Value, then click OK.
The system variables in Table 11 on page 3-73 have reserved
parameter names. Do not use these parameter names when
defining your own parameters.
4
Click Apply to update all the changes to the PARAM
part.
5
Close the Parts spreadsheet.
To use the global parameter in your circuit
Example: To set the independent voltage
source, VCC, to the value of the VSUPPLY
parameter, set its DC property to
{VSUPPLY}.
1
Find the numeric value that you want to replace: a
component value, model parameter value, or other
property value.
2
Replace the value with the name of the global
parameter using the following syntax:
{ global_parameter_name }
The curly braces tell PSpice to evaluate the parameter
and use its value.
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Using global parameters and expressions for values
Expressions
An expression is a mathematical relationship that you can
use to define a numeric or boolean (TRUE/FALSE) value.
PSpice evaluates the expression to a single value every
time:
•
it reads in a new circuit, and
•
a parameter value used within an expression changes
during an analysis.
Example: A parameter that changes with
each step of a DC sweep or parametric
analysis.
Specifying expressions
To use an expression in your circuit
1
Find the numeric or boolean value you want to
replace: a component value, model parameter value,
other property value, or logic in an IF function test (see
page 3-72 for a description of the IF function).
2
Replace the value with an expression using the
following syntax:
{ expression }
where expression can contain any of the following:
•
standard operators listed in Table 9
•
built-in functions listed in Table 10
•
user-defined functions
•
system variables listed in Table 11
•
user-defined global parameters
•
literal operands
The curly braces tell PSpice to evaluate the expression
and use its value.
Example: Suppose you have declared a
parameter named FACTOR (with a value of
1.2) and want to scale a -10 V independent
voltage source, VEE, by the value of
FACTOR. To do this, set the DC property of
VEE to:
{-10*FACTOR}
PSpice evaluates this expression to:
(-10 * 1.2) or -12 volts
For more information on user-defined
functions, see the .FUNC command in the
Commands chapter in the online
OrCA D PSpice A /D Reference
Manual.
For more information on user-defined
parameters, see Using global
parameters and expressions for
values on page 3-67.
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Chapter 3 Preparing a design for simulation
Table 9
Operators in expressions
This operator
class...
Includes this
operator...
arithmetic
+
addition or string
concatenation
-
subtraction
*
multiplication
/
division
**
exponentiation
~
unary NOT
|
boolean OR
^
boolean XOR
&
boolean AND
==
equality test
!=
non-equality test
>
greater than test
>=
greater than or equal to test
<
less than test
<=
less than or equal to test
logical*
relational*
Which means...
* Logical and relational operators are used within the IF() function.
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Using global parameters and expressions for values
Table 10
Functions in arithmetic expressions
This function...
Means this...
ABS(x)
|x|
SQRT(x)
x1/2
EXP(x)
ex
LOG(x)
ln (x)
which is log base e
LOG10(x)
log (x)
which is log base 10
PWR(x,y)
|x|y
PWRS(x,y)
+|x|y (if x > 0)
-|x|y (if x < 0)
SIN(x)
sin(x)
where x is in radians
ASIN(x)
sin-1 (x)
where the result is in
radians
SINH(x)
sinh (x)
where x is in radians
COS(x)
cos (x)
where x is in radians
ACOS(x)
cos-1 (x)
where the result is in
radians
COSH(x)
cosh (x)
where x is in radians
TAN(x)
tan (x)
where x is in radians
ATAN(x)
ARCTAN(x)
tan-1 (x)
where the result is in
radians
ATAN2(y,x)
tan-1 (y/x)
where the result is in
radians
TANH(x)
tanh (x)
where x is in radians
M(x)
magnitude of x*
which is the same as
ABS(x)
P(x)
phase of x*
in degrees; returns 0.0
for real numbers
R(x)
real part of x*
IMG(x)
imaginary part
of x*
which is applicable to
AC analysis only
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Chapter 3 Preparing a design for simulation
Table 10
Functions in arithmetic expressions (continued)
This function...
Means this...
Note In waveform analysis, this function is
D(x).
DDT(x)
time derivative
of x
Note In waveform analysis, this function is
S(x).
SDT(x)
time integral of x which is applicable to
transient analysis
only
TABLE(x,x1,y1,...)
y value as a
function of x
MIN(x,y)
minimum of x
and y
MAX(x,y)
maximum of x
and y
which is applicable to
transient analysis
only
where xn,yn point
pairs are plotted and
connected by straight
lines
LIMIT(x,min,max) min if x < min
max if x > max
else x
Example: {v(1)*STP(TIME-10ns)} gives a
value of 0.0 until 10 nsec has elapsed, then
gives v(1).
SGN(x)
+1 if x > 0
0 if x = 0
-1 if x < 0
STP(x)
1 if x > 0
0 otherwise
which is used to
suppress a value until
a given amount of
time has passed
IF(t,x,y)
x if t is true
y otherwise
where t is a relational
expression using the
relational operators
shown in Table 9
* M(x), P(x), R(x), and IMG(x) apply to Laplace expressions only.
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Using global parameters and expressions for values
Table 11
System variables
This variable...
Evaluates to this...
TEMP
Temperature values resulting from a
temperature, parametric temperature, or DC
temperature sweep analysis.
The default temperature, TNOM, is set in the
Options dialog box (from the Simulation
Settings dialog box, choose the Options tab).
TNOM defaults to 27°C.
Note TEMP can only be used in expressions
pertaining to analog behavioral modelin.
TIME
Time values resulting from a transient
analysis. If no transient analysis is run, this
variable is undefined.
Note If a passive or semiconductor device
has an independent temperature
assignment, then TEMP does not represent
that device’s temperature.
To find out more about customizing
temperatures for passive or semiconductor
devices, refer to the .MODEL command in
the Commands chapter in the online
OrCA D PSpice A /D Reference
Manual.
Note TIME can only be used in analog
behavioral modeling expressions.
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Chapter 3 Preparing a design for simulation
Defining power supplies
For the analog portion of your circuit
To find out how to use these parts and
specify their properties, see the following:
• Setting up a DC stimulus on
page 8-218
• Using VSRC or ISRC parts
on page 3-78
74
If the analog portion of your circuit requires DC power,
then you need to include a DC source in your design. To
specify a DC source, use one of the following parts.
Table 12
For this source type...
Use this part...
voltage
VDC or VSRC
current
IDC or ISRC
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Defining stimuli
Defining stimuli
To simulate your circuit, you need to connect one or more
source parts that describe the input signal that the circuit
must respond to.
The OrCAD libraries supply several source parts that are
described in the tables that follow. These parts depend on:
•
the kind of analysis you are running,
•
whether you are connecting to the analog portion of
your circuit, and
•
how you want to define the stimulus: using the
Stimulus Editor, using a file specification, or by
defining part property values.
Analog stimuli
Analog stimuli include both voltage and current sources.
The following table shows the part names for voltage
sources.
Table 13
If you want this kind of input...
Use this part for voltage...
VDC or VSRC
See Setting up a DC stimulus on
page 8-218 for more details.
VAC or VSRC
See Setting up an AC stimulus on
page 9-233 for more details.
For DC analyses
DC bias
For AC analyses
AC magnitude and phase
For transient analyses
exponential
VEXP or VSTIM*
periodic pulse
VPULSE or VSTIM*
piecewise-linear
VPWL or VSTIM*
piecewise-linear that repeats
forever
VPWL_RE_FOREVER or
VPWL_F_RE_FOREVER**
See Defining a time-based
stimulus on page 10-252 for more
details.
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Chapter 3 Preparing a design for simulation
Table 13
If you want this kind of input...
Use this part for voltage...
piecewise-linear that repeats n
times
VPWL_N_TIMES or
VPWL_F_N_TIMES**
frequency-modulated sine wave
VSFFM or VSTIM*
sine wave
VSIN or VSTIM*
* VSTIM and ISTIM parts require the Stimulus Editor to define the input signal.
** VPWL_F_RE_FOREVER and VPWL_F_N_TIMES are file-based parts; the
stimulus specification is saved in a file and adheres to PSpice netlist syntax.
Example: The current source equivalent to
VDC is IDC, to VAC is IAC, to VEXP is IEXP,
and so on.
To determine the part name for an equivalent current source
1
In the table of voltage source parts, replace the first V
in the part name with I.
Using VSTIM and ISTIM
You can use VSTIM and ISTIM parts to define any kind of
time-based input signal. To specify the input signal itself,
you need to use the Stimulus Editor. See The Stimulus
Editor utility on page 10-253.
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Defining stimuli
If you want to specify multiple stimulus types
If you want to run more than one analysis type, including
a transient analysis, then you need to use either of the
following:
•
time-based stimulus parts with AC and DC properties
•
VSRC or ISRC parts
Using time-based stimulus parts with AC and DC properties
The time-based stimulus parts that you can use to define a
transient, DC, and/or AC input signal are listed below.
VEXP
VPULSE
VPWL
VPWL_F_RE_FOREVER
VPWL_F_N_TIMES
VPWL_RE_FOREVER
VPWL_RE_N_TIMES
VSFFM
VSIN
IEXP
IPULSE
IPWL
IPWL_F_RE_FOREVER
IPWL_F_N_TIMES
IPWL_RE_FOREVER
IPWL_RE_N_TIMES
ISFFM
ISIN
In addition to the transient properties, each of these parts
also has a DC and AC property. When you use one of
these parts, you must define all of the transient properties.
However, it is common to leave DC and/or AC undefined
(blank). When you give them a value, the syntax you need
to use is as follows.
Table 14
This property...
Has this syntax...
DC
DC_value[units]
AC
magnitude_value[units] [phase_value]
For the meaning of transient source
properties, refer to the I/V (independent
current and voltage source) device type
syntax in the A nalog Devices chapter
in the online OrCA D PSpice A /D
Reference Manual.
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Chapter 3 Preparing a design for simulation
Using VSRC or ISRC parts
The VSRC and ISRC parts have one property for each
analysis type: DC, AC, and TRAN. You can set any or all
of them using PSpice netlist syntax. When you give them
a value, the syntax you need to use is as follows.
Table 15
For the syntax and meaning of transient
source specifications, refer to the I/V
(independent current and voltage source)
device type in the A nalog Devices
chapter in the online OrCA D PSpice
A /D Reference Manual.
78
This property...
Has this syntax...
DC
DC_value[units]
AC
magnitude_value[units] [phase_value]
TRAN
time-based_type (parameters)
where time-based_type is EXP, PULSE, PWL,
SFFM, or SIN, and the parameters depend on the
time-based_type.
Note
OrCAD recommends that if you are running only a transient
analysis, use a VSTIM or ISTIM part if you have the standard
package, or one of the other time-based source parts that has
properties specific for a waveform shape.
Pspug.book Page 79 Wednesday, November 11, 1998 1:14 PM
Things to watch for
Things to watch for
This section includes troubleshooting tips for some of the
most common reasons your circuit design may not netlist
or simulate.
For a roadmap to other commonly
encountered problems and solutions, see
When netlisting fails or the
simulation does not start on
page 3-58.
Unmodeled parts
If you see messages like this in the PSpice Simulation
Output window,
Warning: Part part_name has no simulation
model.
then you may have done one of the following things:
•
Placed a part from the OrCAD libraries that is not
available for simulation (used only for board layout).
•
Placed a custom part that has been incompletely
defined for simulation.
Do this if the part in question is from the OrCAD
libraries
•
•
Replace the part with an equivalent part from one of
the libraries listed in the tables below.
Make sure that you can simulate the part by checking
the following:
•
That it has a PSPICETEMPLATE property and that
its value is non-blank.
•
That it has an Implementation Type = PSpice
MODEL property and that its Implementation
property is non-blank.
The libraries listed in the tables that follow
all contain parts that you can simulate.
Some files also contain parts that you can
only use for board layout. That’s why you
need to check the Pspice TEMPLATE
property if you are unsure or still getting
warnings when you try to simulate your
circuit.
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Chapter 3 Preparing a design for simulation
Table 16
To find out more about a particular library,
refer to the online Library List or read
the header of the model library file itself.
80
Analog libraries with modeled parts (installed in Capture\Library\PSpice)
1_SHOT
EPWRBJT
NAT_SEMI
ABM
FILTSUB
OPAMP
ADV_LIN
FWBELL
OPTO
AMP
HARRIS
PHIL_BJT
ANALOG
IGBT
PHIL_FET
ANA_SWIT
JBIPOLAR
PHIL_RF
ANLG_DEV
JDIODE
POLYFET
ANL_MISC
JFET
PWRBJT
APEX
JJFET
PWRMOS
BIPOLAR
JOPAMP
SIEMENS
BREAKOUT
JPWRBJT
SWIT_RAV
BUFFER
JPWRMOS
SWIT_REG
BURR_BRN
LIN_TECH
TEX_INST
CD4000
MAGNETIC
THYRISTR
COMLINR
MAXIM
TLINE
DIODE
MOTORAMP
XTAL
EBIPOLAR
MOTORMOS
ZETEX
EDIODE
MOTORSEN
ELANTEC
MOTOR_RF
Pspug.book Page 81 Wednesday, November 11, 1998 1:14 PM
Things to watch for
Check for this if the part in question is custom-built
Are there blank (or inappropriate) values for the part’s
Implementation and PSPICETEMPLATE properties?
If so, load this part into the part editor and set these
properties appropriately. One way to approach this is to
edit the part that appears in your design.
To edit the properties for the part in question
1
In the schematic page editor, select the part.
2
From the Edit menu, choose Part.
The part editor window appears with the part already
loaded.
3
From the Edit menu, choose Properties and proceed to
change the property values.
To find out more about setting the
simulation properties for parts, see
Defining part properties needed
for simulation on page 5-139.
To find out more about using the part
editor, refer to your OrCA D Capture
User’s Guide.
Unconfigured model, stimulus, or include files
If you see messages like these in the PSpice Simulation
Output window,
(design_name) Floating pin: refdes pin
pin_name
Floating pin: pin_id
File not found
Can’t open stimulus file
or messages like these in the PSpice output file,
Model model_name used by device_name is
undefined.
Subcircuit subckt_name used by device_name
is undefined.
Can’t find .STIMULUS “refdes” definition
then you may be missing a model library, stimulus file, or
include file from the configuration list, or the configured
file is not on the library path.
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Chapter 3 Preparing a design for simulation
Check for this
•
Does the relevant model library, stimulus file, or
include file appear in the configuration list?
•
If the file is configured, does the default library search
path include the directory path where the file resides,
or explicitly define the directory path in the
configuration list?
To find out more about how to configure
these files and about search order, see
Configuring model libraries on
page 4-120.
If the file is not configured, add it to the list and make sure
that it appears before any other library or file that has an
identically-named definition.
To find out more about the default
configuration, see How are models
organized? on page 4-88.
To view the configuration list
1
In the Simulation Settings dialog box, click the Include
Files tab.
If the directory path is not specified, update the
default library search path or change the file entry in
the configuration list to include the full path
specification.
To find out more about the library search
path, see Changing the library
search path on page 4-125.
To view the default library search path
1
In the Simulation Settings dialog box, click the
Libraries tab.
Unmodeled pins
If you see messages like these in the PSpice Simulation
Output window,
Warning: Part part_name pin pin_name is
unmodeled.
Warning: Less than 2 connections at node
node_name.
or messages like this in the PSpice output file,
Floating/unmodeled pin fixups
then you may have drawn a wire to an unmodeled pin.
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Things to watch for
The OrCAD libraries include parts that are suitable for
both simulation and board layout. The unmodeled pins
map into packages but have no electrical significance;
PSpice ignores unmodeled pins during simulation.
Check for this
Are there connections to unmodeled pins?
If so, do one of the following:
•
Remove wires connected to unmodeled pins.
•
If you expect the connection to affect simulation
results, find an equivalent part that models the pins in
question and draw the connections.
To find out more about searching for parts,
see Finding the part that you want
on page 3-62.
Missing ground
If for every net in your circuit you see this message in the
PSpice output file,
ERROR -- Node node_name is floating.
then your circuit may not be tied to ground.
Check for this
Are there ground parts named 0 (zero) connected
appropriately in your design?
If not, place and connect one (or more, as needed) in your
design. You can use the 0 (zero) ground part in
SOURCE.OLB or any other ground part as long as you
change its name to 0.
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Chapter 3 Preparing a design for simulation
Missing DC path to ground
If for selected nets in your circuit you see this message in
the PSpice output file,
ERROR -- Node node_name is floating.
then you may be missing a DC path to ground.
Check for this
Are there any nets that are isolated from ground by either
open circuits or capacitors?
If so, then add a very large (for example, 1 Gohm) resistor
either:
Note When calculating the bias point
solution, PSpice treats capacitors as open
circuits and inductors as short circuits.
•
in parallel with the capacitor or open circuit, or
•
from the isolated net to ground.
Example: The circuit shown below connects capacitors
(DC open circuits) such that both ends of inductor L2 are
isolated from ground.
When simulated, PSpice flags nets 2 and 3 as floating. The
following topology solves this problem.
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Creating and editing models
4
Chapter overview
This chapter provides information about creating and
editing models for parts that you want to simulate.
Topics are grouped into four areas introduced later in this
overview. If you want to find out quickly which tools to
use to complete a given task and how to start, then:
1
Go to the roadmap in Ways to create and edit models on
page 4-92.
2
Find the task you want to complete.
3
Go to the sections referenced for that task for more
information about how to proceed.
Background information These sections present
model library concepts and an overview of the tools that
you can use to create and edit models:
•
What are models? on page 4-87
•
How are models organized? on page 4-88
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Chapter 4 Creating and editing models
•
Tools to create and edit models on page 4-91
Task roadmap This section helps you find other
sections in this chapter that are relevant to the model
editing task that you want to complete:
•
Ways to create and edit models on page 4-92
How to use the tools These sections explain how to
use different tools to create and edit models on their own
and when editing schematic pages or parts:
•
Using the Model Editor to edit models on page 4-93
•
Editing model text on page 4-110
•
Using the Create Subcircuit command on page 4-115
Other useful information These sections explain
how to configure and reuse models after you have created
or edited them:
86
•
Changing the model reference to an existing model
definition on page 4-117
•
Reusing instance models on page 4-118
•
Configuring model libraries on page 4-120
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What are models?
What are models?
A model defines the electrical behavior of a part. On a
schematic page, this correspondence is defined by a part’s
Implementation property, which is assigned the model
name.
Depending on the device type that it describes, a model is
defined as on of the following:
•
a model parameter set
•
a subcircuit netlist
Both ways of defining a model are text-based, with
specific rules of syntax.
Models defined as model parameter sets
PSpice has built-in algorithms or models that describe the
behavior of many device types. The behavior of these
built-in models is described by a set of model parameters.
You can define the behavior for a device that is based on a
built-in model by setting all or any of the corresponding
model parameters to new values using the PSpice
.MODEL syntax. For example:
.MODEL MLOAD NMOS
+ (LEVEL=1 VTO=0.7 CJ=0.02pF)
The .MODEL syntax applies to the analog
models built in to PSpice.
Models defined as subcircuit netlists
For some devices, there are no PSpice built-in models that
can describe their behavior fully. These types of devices
are defined using the PSpice .SUBCKT/.ENDS or
subcircuit syntax instead.
To find out more about PSpice command
and netlist syntax, refer to the online
OrCA D PSpice A /D Reference
Manual.
Subcircuit syntax includes:
•
Netlists to describe the structure and function of the
part.
•
V ariable input parameters to fine-tune the model.
For example:
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Chapter 4 Creating and editing models
* FIRST ORDER RC STAGE
.SUBCKT LIN/STG IN OUT AGND
+ PARAMS: C1VAL=1 C2VAL=1 R1VAL=1 R2VAL=1
+
GAIN=10000
C1 IN N1
{C1VAL}
C2 N1 OUT {C2VAL}
R1 IN N1
{R1VAL}
R2 N1 OUT {R2VAL}
EAMP1 OUT AGND VALUE={V(AGND,N1)*GAIN}
.ENDS
How are models organized?
The key concepts behind model organization are as
follows:
•
Model definitions are saved in files called model
libraries.
•
Model libraries must be configured so that PSpice
searches them for definitions.
•
Depending on the configuration, model libraries are
available either to a specific design or to all (global)
designs.
Model libraries
You can use the OrCAD Model Editor, or any
standard text editor, to view model
definitions in the libraries.
Device model and subcircuit definitions are organized
into model libraries. Model libraries are text files that
contain one or more model definitions. Typically, model
library names have a .LIB extension.
For example: MOTOR_RF.LIB contains
models for Motorola-made RF bipolar
transistors.
Most model libraries contain models of similar type. For
vendor-supplied models, libraries are also partitioned by
manufacturer. To find out more about the models
contained in a model library, read the comments in the file
header.
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How are models organized?
Model library configuration
PSpice searches model libraries for the model names
specified by the MODEL implementation for parts in your
design. These are the model definitions that PSpice uses to
simulate your circuit.
For PSpice to know where to look for these model
definitions, you must configure the libraries. This means:
•
Specifying the directory path or paths to the model
libraries.
•
Naming each model library that PSpice should search
and listing them in the needed search order.
•
Assigning global or design scope to the model library.
Global vs. design models and libraries
Model libraries and the models they contain have either
design or global application to your designs.
To optimize the search, PSpice uses
indexes. To find out more about this and
how to add, delete, and rearrange
configured libraries, see Configuring
model libraries on page 4-120.
To find out how to change the design and
global configuration of model libraries, see
Changing design and global
scope on page 4-123.
Design models
Design models apply to one design.
The schematic page editor automatically creates a design
model whenever you modify the model definition for a
part instance on your schematic page. You can also create
models externally and then manually configure the new
libraries for a specific design.
Example usage: To set up device and lot
tolerances on the model parameters for a
particular part instance when running a
Monte Carlo or sensitivity/worst-case
analysis.
Global models
PSpice searches design libraries before
global libraries. To find out more, see
Changing model library search
order on page 4-124.
Global models are available to all
designs you create. The part editor automatically creates a
global model whenever you create a part with a new
model definition. The Model Editor also creates global
models. You can also create models externally and then
manually configure the new libraries for use in all designs.
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Chapter 4 Creating and editing models
Nested model libraries
Besides model and subcircuit definitions, model libraries
can also contain references to other model libraries using
the PSpice .LIB syntax. When searching model libraries for
matches, PSpice also scans these referenced libraries.
Example: Suppose you have two custom model libraries,
MYDIODES.LIB and MYOPAMPS.LIB, that you want
PSpice to search any time you simulate a design. Then you
can create a third model library, MYMODELS.LIB, that
contains these two statements:
.LIB mydiodes.lib
.LIB myopamps.lib
and configure MYMODELS.LIB for global use. Because
MYDIODES.LIB and MYOPAMPS.LIB are referenced
from MYMODELS.LIB, they are automatically configured
for global use as well.
For a list of device models provided by
OrCAD, refer to the online Library List.
OrCAD-provided models
The model libraries that you initially install with your
OrCAD programs are listed in NOM.LIB. This file
demonstrates how you can nest references to other
libraries and models.
If you click the Libraries tab in the Simulation Settings
dialog box immediately after installation, you see the
NOM.LIB* entry in the Library Files list. The asterisk
means that this model library, and any of the model
libraries it references, contain global model definitions.
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Tools to create and edit models
Tools to create and edit models
There are three tools that you can use to create and edit
model definitions. Use the:
•
•
Note
Model Editor when you want to:
•
derive models from data sheet curves provided by
manufacturers, or
•
modify the behavior of a Model Editor-supported
model.
•
edit the PSpice command syntax (text) for
.MODEL and .SUBCKT definitions.
Create Subcircuit command in the schematic page
editor when you have a hierarchical level in your
design that you want to set up as an equivalent part
with behavior described as a subcircuit netlist
(.SUBCKT syntax).
If you created a subcircuit definition using the Create Subcircuit
command and want to alter it, use the Model Editor to edit the
definition, or modify the original hierarchical schematic and run
Create Subcircuit again to replace the definition.
For a description of models supported by
the Model Editor, see Model
Editor-supported device types on
page 4-95.
Note The Create Subcircuit command does
not help you create a hierarchical design.
You need to create this yourself before
using the Create Subcircuit command. For
information on hierarchical designs and
how to create them, refer to the OrCA D
Capture User’s Guide.
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Chapter 4 Creating and editing models
Ways to create and edit models
This section is a roadmap to other information in this
chapter. Find the task that you want to complete, then go
to the referenced sections for more information.
If you want to...
Then do this...
To find out more, see this...
➥ Create or edit the model
Create or load the part first in
the part editor, then edit the
model using the Model
Editor *.
Running the Model Editor
from the schematic page editor
on page 4-101..
Start the Model Editor * and
enable/disable automatic part
creation as needed; then create
or view the model.
Running the Model Editor
alone on page 4-99.
Select the part instance on your
schematic, then edit the model
using the Model Editor.
Starting the Model Editor from
the schematic page editor in
Capture on page 4-111.
Select the part instance on your
schematic page, then edit the
model using the Model
Editor *.
Running the Model Editor
from the schematic page editor
on page 4-101
Starting the Model Editor from
the schematic page editor in
Capture on page 4-111.
Use the Create Subcircuit
command in the schematic
page editor.
Using the Create Subcircuit
command on page 4-115.
for an existing part and
have it affect all designs that
use that part.
➥ Create a model from
scratch and
automatically create a
part for it to use in any
design.
➥ Create a model from
scratch without a part
and have the model
definition available to any
design.
➥ View model
characteristics for a part.
➥ Define tolerances on
model parameters for
statistical analyses.
➥ Test behavior
variations on a part.
➥ Refine a model before
making it available to all
designs.
➥ Derive subcircuit
definitions from a
hierarchical design.
* For a list of device types that the Model Editor supports, see Model Editor-supported device types on page 4-95.
If the Model Editor does not support the device type for the model definition that you want to create, then you can edit the text
using the Model Editor to create a model definition using the PSpice .MODEL and .SUBCKT command syntax. Remember to
configure the new model library.
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Using the Model Editor to edit models
Using the Model Editor to
edit models
The Model Editor converts information that you enter
from the device manufacturer’s data sheet into either:
•
model parameter sets using PSpice .MODEL syntax,
or
•
subcircuit netlists using PSpice .SUBCKT syntax,
and saves these definitions to model libraries that PSpice
can search when looking for simulation models.
model libraries
OrCAD
Capture
The Normal view in the Model Editor does
not support the following subcircuit
constructs:
• optional nodes construct, OPTIONAL:
• variable parameters construct,
PARAMS:
OrCAD
PSpice
OrCAD Model Editor
MODEL
+ BF =
• local .PARAM command
• local .FUNC command
model
definitions
exported
model file
To refine the subcircuit definition for these
constructs, use the Model Text view in
Model Editor, described in Editing
model text on page 4-110.
Figure 27 Relationship of the Model Editor to Capture and
PSpice.
Note
By default, the Model Editor creates or updates model libraries. To
create an exported model file, choose the Export command from
the Model menu and configure it as an include file. For more
information, see How PSpice uses model libraries and the
companion sidebar on page 4-121.
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Chapter 4 Creating and editing models
Ways to use the Model Editor
You can use the Model Editor five ways:
To find out more, see Running the
Model Editor alone on
page 4-99.
•
To define a new model, and then automatically
create a part. Any new models and parts are
automatically available to any design.
To find out more, see Running the
Model Editor alone on
page 4-99.
•
To define a new model only (no part). You can
optionally turn off the part creation feature for new
models. The model definition is available to any
design, for example, by changing the model
implementation for a part instance.
To find out more, see Running the
Model Editor from the
schematic page editor on
page 4-101.
•
To edit a model definition for a part instance on your
schematic. This means you need to start the Model
Editor from the schematic page editor after selecting a
part instance on your schematic. The schematic editor
automatically attaches the new model implementation
(that the Model Editor creates) to the selected part
instance.
To find out more, see Running the
Model Editor alone on
page 4-99.
•
To examine or verify the electrical characteristics of
a model without running PSpice. This means you can
use the Model Editor alone to:
94
•
check characteristics of a model quickly, given a
set of model parameter values, or
•
compare characteristic curves to data sheet
information or measured data.
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Using the Model Editor to edit models
Model Editor-supported device types
Table 17 summarizes the device types supported in the
Model Editor.
Table 17
Models supported in the Model Editor
This part type...
Uses this
definition form...
And this
name prefix*...
diode
.MODEL
D
bipolar transistor
.MODEL
Q
bipolar transistor,
Darlington model
.SUBCKT
X
IGBT
.MODEL
Z
JFET
.MODEL
J
power MOSFET
.MODEL
M
operational amplifier**
.SUBCKT
X
voltage comparator**
.SUBCKT
X
nonlinear magnetic core
.MODEL
K
voltage regulator**
.SUBCKT
X
voltage reference**
.SUBCKT
X
Device types that the Model Editor models
using the .MODEL statement are based on
the models built into PSpice.
Note The model parameter defaults used
by the Model Editor are different from
those used by the models built into PSpice.
* This is the standard PSpice device letter notation. Refer to the online OrCA D
PSpice A /D Reference Manual.
** The Model Editor only supports .SUBCKT models that were generated by the
Model Editor. However, you can edit the text of a .SUBCKT model created
manually, or by another tool, using the Model Editor. When you load a
.SUBCKT model that the Model Editor did not create, the Model Editor
displays the text of the model for editing.
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Chapter 4 Creating and editing models
Ways To Characterize Models
Testing and verifying
models created with the
Model Editor
Each curve in the Model Editor is defined
only by the parameters being adjusted. For
the diode, the forward current curve only
shows the part of the current equation that
is associated with the forward characteristic
parameters (such as IS, N, Rs).
However, PSpice uses the full equation for
the diode model, which includes a term
involving the reverse characteristic
parameters (such as ISR, NR). These
parameters could have a significant effect
at low current.
This means that the curve displayed in the
Model Editor does not exactly match what is
displayed in PSpice after a simulation. Be
sure to test and verify models using PSpice.
If needed, fine-tune the models.
Figure 28 shows two ways to characterize models using
the Model Editor.
device data from
data sheets
parts
estimation
model
parameters
PSpice
simplified
equation
evaluation
graph of device
characteristic
user
data-entry
“what-if” model data
Figure 28 Process and data flow for the Model Editor.
Creating models from data sheet information
Note When specifying operating
characteristics for a model, you can use
typical values found on data sheets
effectively for most simulations. To verify
your design, you may also want to use
best- and worst-case values to create
separate models, and then swap them into
the circuit design.
96
The most common way to characterize models is to enter
data sheet information for each device characteristic. After
you are satisfied with the behavior of each characteristic,
you can have the Model Editor estimate (or extract) the
corresponding model parameters and generate a graph
showing the behavior of the characteristic. This is called
the fitting process.
You can repeat this process, and when you are satisfied
with the results, save them; the Model Editor creates
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Using the Model Editor to edit models
model libraries containing appropriate model and
subcircuit definitions.
Analyzing the effect of model parameters
on device characteristics
You can also edit model parameters directly and see how
changing their values affects a device characteristic. As
you change model parameters, the Model Editor
recalculates the behavior of the device characteristics and
displays a new curve for each of the affected ones.
How to fit models
For a given model, the Model Editor displays a list of the
device characteristics and a list of all model parameters
and performance curves (see Figure 29).
For more information about the
characteristics of devices supported by the
Model Editor, refer to the online OrCA D
PSpice A /D Reference Manual.
Figure 29 Model Editor workspace with data for a bipolar
transistor.
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Chapter 4 Creating and editing models
To fit the model
1
2
For each device characteristic that you want to set up:
a
In the Spec Entry frame, click the tab of the device
characteristic.
b
Enter the device information from the data sheet.
From the Tools menu, choose Extract Parameters to
extract all relevant model parameters for the current
specification.
A check mark appears in the Active column of the
Parameters frame for each extracted model parameter.
3
Repeat steps 1-2 until the model meets target
behaviors.
To view updated performance curves
1
Note
98
On the toolbar, click the Update Graph button.
If you view performance curves before fitting, then your data
points and the curve for the current model specification may not
match.
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Using the Model Editor to edit models
Running the Model Editor alone
Run the Model Editor alone if you want to do any of the
following:
•
create a model and use the model in any design (and
automatically create a part),
•
create a model and have the model definition available
to any design (without creating a part), or
•
examine or verify the characteristics of a given model
without using PSpice.
After you have selected the part that you
want to model, you can proceed with
entering data sheet information and model
fitting as described in How to fit
models on page 4-97.
Running the Model Editor alone means that the model
you are creating or examining is not currently tied to a
part instance on your schematic page or to a part editing
session.
Note
You can only edit models for device types that the Model Editor
supports. See Model Editor-supported device types on
page 4-95 for details.
Starting the Model Editor
To start the Model Editor alone
1
From the Start menu, point to the OrCAD program
folder, then choose Model Editor.
2
From the File menu, choose New or Open, and enter
an existing or new model library name.
3
From the Part menu, choose New, Copy From, or
Import to load a model.
If you have already started the Model
Editor from Capture and want to continue
working on new models, then:
1 Save the opened model library.
2 Open or create a different model
library.
3 Get a model, or create a new one.
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Chapter 4 Creating and editing models
Enabling and disabling automatic part creation
Instead of using the OrCAD default part set
for new models, you can have the Model
Editor use your own set of standard parts.
To find out more, see Basing new
parts on a custom set of parts on
page 5-133.
Part creation in the Model Editor is optional. By default,
automatic part creation is enabled. However, if you
previously disabled part creation, you will need to enable
it before creating a new model and part.
To automatically create parts for new models
1
From the Tools menu, choose Options.
2
If not already checked, select Always Create Part to
enable automatic part creation.
3
Under Save Part To, enter the name of the part library
for the new part. Choose either:
Example: If the model library is
MYPARTS.LIB, then the Model Editor
creates the part library MYPARTS.OLB.
If you want to save the open model library
to a new library, then:
Note
•
Part Library Path Same As Model Library to create
or open the *.OLB file that has the same name
prefix as the currently open model library (*.LIB).
•
User-Defined Part Library, and then enter a file
name in the Part Library Name text box.
If you select a user-defined Part library, the Model Editor saves all
new parts to the specified file until you change it.
1 From the File menu, choose Save As.
2 Enter the name of the new model
library.
If you want to save only the model
definition that you are currently editing to
a different library, then
1 From the Part menu, select Export.
2 Enter the name of the new file.
3 If you want PSpice to search this file
automatically, configure it in Capture
(using the Libraries tab on the
Simulation Settings dialog box).
100
Saving global models (and parts)
When you save your changes, the Model Editor does the
following for you:
•
Saves the model definition to the model library that
you originally opened.
•
If you had the automatic part creation option enabled,
saves the part definition to
MODEL_LIBRARY_NAME.OLB.
To save the new model (and part)
1
From the File menu, choose Save to update
MODEL_LIBRARY_NAME.LIB (and, if you enabled
part creation, MODEL_LIBRARY_NAME.OLB), and
save them to disk.
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Using the Model Editor to edit models
Running the Model Editor from the
schematic page editor
If you want to:
•
test behavior variations on a part, or
•
refine a model before making it available to all
designs,
Once you have started the Model Editor ,
you can proceed with entering data sheet
information and model fitting as described
in How to fit models on
page 4-97.
then run the Model Editor from the schematic page editor
in Capture.
This means editing models for part instances on your
schematic page. When you select a part instance and edit
its model, the schematic page editor automatically creates
an instance model that you can then change.
Note
You can only edit models for device types that the Model Editor
supports. See Model Editor-supported device types on
page 4-95 for details.
What is an instance model?
An instance model is a copy of the part’s original model.
The copied model is local to the design. You can
customize the instance model without impacting any
other design that uses the original part from the library.
For more information on instance models,
see Reusing instance models on
page 4-118.
When the schematic editor creates the copy, it assigns a
unique name that is by default:
original_model_name-Xn
where n is <blank 1 | 2 | ... > depending on the number of
different instance models derived from the original model
for the current design.
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Chapter 4 Creating and editing models
Starting the Model Editor
To start editing an instance model
To find out how Capture searches the
library, see Changing model library
search order on page 4-124.
1
In Capture, select one part on your schematic page.
2
From the Edit menu, choose PSpice Model.
The schematic page editor searches the model libraries
for the instance model.
•
If found, the schematic page editor starts the Model
Editor, which opens the model library that contains
the instance model and loads the instance model.
•
If not found, the schematic page editor assumes that
this is a new instance model and does the following:
makes a copy of the original model definition, names
it original_model_name-Xn, and starts the Model Editor
with the new model loaded.
Saving design models
When you save your edits, the Model Editor saves the
model definition to DESIGN_NAME.LIB, which is already
configured for local use (see What happens if you don’t save
the instance model on page 4-103).
To save instance models
1
102
From the File menu, choose Save to update
DESIGN_NAME.LIB and save it to disk.
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Using the Model Editor to edit models
What happens if you don’t save the instance model
Before the schematic page editor starts the Model Editor,
it does these things:
•
Makes a copy of the original model and saves it as an
instance model in SCHEMATIC_NAME.LIB.
•
Configures SCHEMATIC_NAME.LIB for design use, if
not already done.
•
Attaches the new instance model name to the
Implementation property for the selected part
instance.
This means that if you:
•
quit the Model Editor, or
•
return to Capture to simulate the design
without first saving the model you are editing, the part
instance on your schematic page is still attached to the
instance model implementation.
In this case, the instance model is identical to the original
model. If you decide to edit this model later, be sure to do
one of the following:
•
If you want the changes to remain specific to the
current design, edit the instance model in the design
library, using the Model Editor.
•
If you want the change to be global, change the model
implementation for the part instance in your design
back to the original model name in the global library,
and then edit the original model from within the part
editor.
To find out how to change model
references, see Changing the model
reference to an existing model
definition on page 4-117.
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Chapter 4 Creating and editing models
The Model Editor tutorial
In this tutorial, you will model a simple diode device as
follows:
•
Create the schematic for a simple half-wave rectifier.
•
Run the Model Editor from the schematic editor to
create an instance model for the diode in your
schematic.
Creating the half-wave rectifier design
To draw the design
press P
Figure 30 Design for a half-wave rectifier.
press W
1
From the Project Manager, from the File menu point to
New, then choose Project.
2
Enter the name of the new project (RECTFR) and click
Create.
3
From Capture’s Place menu, choose Part.
4
Place one each of the following parts (reference
designator shown in parentheses) as shown in
Figure 30:
Dbreak (D1 diode)
•
C (C1 capacitor)
•
R (R1 resistor)
•
VSIN (V1 sine wave source)
5
Click the Ground button and place the analog ground.
6
From the Place menu, choose Wire, and draw the
connections between parts as shown in Figure 30.
7
From the File menu, choose Save.
Note
104
•
If you were to simulate this design using a transient analysis, you
would also need to set up a transient specification for V1; most
likely, this would mean defining the VOFF (offset voltage), VAMPL
(amplitude), and FREQ (frequency) properties for V1. For this
tutorial, however, you will not perform a simulation, so you can
skip this step.
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Using the Model Editor to edit models
Using the Model Editor to edit the D1 diode model
To create a new model and model library
1
In the Model Editor, from the Model menu, choose
New.
2
In the New dialog box, do the following:
a
In the Model text box, type DbreakX.
b
From the From Model list, select Diode.
c
Click OK.
3
From the File menu, choose Save As.
4
In the File name text box, type rectfr.lib to save the
library as RECTFR.LIB.
Entering data sheet information
As shown in Figure 31, the Model Editor initially displays:
•
diode model characteristics listed in the Models List
frame, and
•
DbreakX model parameter values listed in the
Parameters frame.
Figure 31 Model characteristics and parameter values for
DbreakX.
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Chapter 4 Creating and editing models
You can modify each model characteristic shown in the
Model Spec frame with new values from the data sheets.
The Model Editor takes the new information and fits new
model parameter values.
When updating the entered data, the Model Editor
expects either:
•
device curve data (point pairs), or
•
single-valued data,
depending on the device characteristic.
For the diode, Forward Current, Junction Capacitance,
and Reverse Leakage require device curve data. Reverse
Breakdown and Reverse Recovery require single-valued
data.
Table 1 lists the data sheet information for the Dbreak-X
model.
Table 1
Sample diode data sheet values
For this model characteristic...
Enter this...
forward current
(1.3, 0.2)
junction capacitance
(1m, 120p) (1, 73p) (3.75, 45p)
reverse leakage
(6, 20n)
reverse breakdown
(Vz=7.5, Iz=20m, Zz=5)
reverse recovery
no changes
To change the Forward Current characteristic
1
In the Spec Entry frame, click the Forward Current tab.
This tab requires curve data.
106
2
In the Vfwd text box, type 1.3.
3
Press F to move to the Ifwd text box, and then type
0.2.
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Using the Model Editor to edit models
To change the values for Junction Capacitance and
Reverse Leakage
1
Follow the same steps as for Forward Current,
entering the data sheet information listed in Table 1
that corresponds to the current model characteristic.
To change the Reverse Breakdown characteristic
1
In the Spec Editing frame, click the Reverse
Breakdown tab.
This tab requires single-valued data.
2
In the Vz text box, type 7.5.
3
Press F to move to the Iz text box, and then type 20m.
4
Press F to move to the Zz text box, and then type 5.
The Model Editor accepts the same scale
factors normally accepted by PSpice.
Extracting model parameters
To generate new model parameter values
1
From the Tools menu, choose Extract Parameters.
A check mark appears in the Active column of the
Parameters frame for each extracted model parameter.
To display the curves for the five diode characteristics
1
From the Window menu, choose Tile.
Some of the plots are shown in Figure 32 below.
You can also do the following with an active
plot window:
• Pan and zoom within the plot using
commands on the View menu.
• Rescale axes using the Axis Settings
command on the Plot menu.
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Chapter 4 Creating and editing models
Figure 32 Assorted device characteristic curves for a diode.
Adding curves for more than one temperature
By default, the Model Editor computes device curves at
27°C. For any characteristic, you can add curves to the plot
at other temperatures.
To add curves for Forward Current at a different temperature
1
In the Spec Entry frame, click the Forward Current tab.
2
From the Plot menu, choose Add Trace.
3
Type 100 (in °C).
4
Click OK.
The Forward Current plot should appear as shown in
Figure 33 below.
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Using the Model Editor to edit models
Figure 33 Forward Current device curve at two temperatures.
Completing the model definition
You can refine the model definition by:
•
modifying the entered data as described before, or
•
editing model parameters directly.
You can update individual model parameters by editing
them in the Parameters frame of the Model Editor
workspace. When you save the model library, the Model
Editor automatically updates the device curves.
For this tutorial, leave the model parameters at their
current settings.
To save the model definition with the current parameter values
and to make the model available to your design
1
From the File menu, select Save to update
RECTFR.LIB and save the library to disk.
Your design is ready to simulate with the model
definition you just created.
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Chapter 4 Creating and editing models
Editing model text
Caution—If you edit the text of a
model that was created by entering data
sheet values, you may not be able to edit
the model in Normal view again.
For any model, you can edit model text in the Model
Editor instead of using the Spec Entry and Parameter
frames. However, there are two cases where you must edit
the model text:
•
When you want to edit models of device types not
supported by the Model Editor. The model text is
displayed automatically when you load one of these
models.
•
When you want to add DEV and LOT tolerances to a
model for Monte Carlo or sensitivity/worst-case
analysis.
By typing PSpice commands and netlist entries, you can
do the following:
•
change definitions, and
•
create new definitions
When you are finished, the Model Editor automatically
configures the model definitions into the model libraries.
To display the model text
1
To find out more about PSpice command
and netlist syntax, refer to the online
OrCA D PSpice A /D Reference
Manual.
From the View menu, choose Model Text.
The Model Editor displays the PSpice syntax for
model definitions:
•
.MODEL syntax for models defined as parameter
sets
•
.SUBCKT syntax for models defined as netlist
subcircuits
You can edit the definition just as you would in any
standard text editor.
Editing .MODEL definitions
For definitions implemented as model parameter sets
using PSpice .MODEL syntax, the Model Editor lists one
parameter per line. This makes it easier to add DEV/LOT
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Editing model text
tolerances to model parameters for Monte Carlo or
sensitivity/worst-case analysis.
Editing .SUBCKT definitions
For definitions implemented as subcircuit netlists using
PSpice .SUBCKT syntax, the model editor displays the
subcircuit syntax exactly as it appears in the model
library. The Model Editor also includes all of the
comments immediately before or after the subcircuit
definition.
Changing the model name
You can change the model name directly in the PSpice
.MODEL or .SUBCKT syntax, but double-check that the
new name does not conflict with models already
contained in the libraries.
Note
If you do create a model with the same name as another model and
want PSpice to always use your model, make sure the configured
model libraries are ordered so your definition precedes any other
definitions.
To find out more about instance model
naming conventions, see What is an
instance model? on page 4-112.
To find out more about search order in the
model library, see Changing model
library search order on
page 4-124.
Starting the Model Editor
from the schematic page editor in Capture
Start the model editor from the schematic page editor in
Capture when you want to:
•
define tolerances on model parameters for statistical
analyses,
•
test behavior variations on a part, or
•
refine a model before making it available to all
designs.
You can also use the model editor to view
the syntax for a model definition. When
you are finished viewing, be sure to quit the
Model Editor without saving the library, so
the schematic page editor does not create
an instance model.
This means editing models for part instances in your
design. When you select a part instance and edit its model,
the schematic page editor automatically creates an instance
model that you can then change.
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Chapter 4 Creating and editing models
For more information on instance models,
see Reusing instance models on
page 4-118.
What is an instance model?
An instance model is a copy of the part’s original model.
The copied model is limited to use in the current design.
You can customize the instance model without impacting
any other design that uses the original part from the
library.
When the schematic page editor creates the copy, it
assigns a unique name that is by default:
original_model_name-Xn
where n is <blank 1 | 2 | ... > depending on the number of
different instance models derived from the original model
for the current design.
Starting the Model Editor
After you start the Model Editor, you can
proceed to change the text as described in
To display the model text on
page 4-110.
To find out how Capture searches the
library, see Changing model library
search order on page 4-124.
112
To start editing an instance model
1
In the schematic page editor, select the part on the
schematic page.
2
From the Edit menu, choose PSpice Model.
The schematic page editor searches the configured
libraries for the instance model:
•
If found, the schematic page editor starts the
Model Editor, which opens the library containing
the instance model and displays the model for
editing.
•
If not found, the schematic page editor assumes
that this is a new instance model and starts the
Model Editor, which does the following: makes a
copy of the original model definition, names it
original_model_name-Xn, and displays the new
model text for editing.
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Editing model text
Saving design models
When you save your edits, the following is done for you
to make sure the instance model is linked to the selected
part instances in your design:
•
The Model Editor saves the model definition to
DESIGN_NAME.LIB.
•
If the library is new, the Model Editor configures
DESIGN_NAME.LIB for local use.
•
The schematic page editor assigns the new model
name to the Implementation property for each of the
selected part instances.
Actions that automatically
configure the instance
model library for global use
instead
Instance model libraries are normally
configured for design use. However, if you
perform the following action, the model
editor configures the library for global use
instead:
• Save the model to a different library
by typing a new file name in the
Library text box in the Save To frame.
To save instance models
1
In the Model Editor, from the File menu, choose Save.
2
From the File menu, choose Exit to quit the Model
Editor.
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Chapter 4 Creating and editing models
Example: editing a Q2N2222 instance model
Suppose you have a design named MY.OPJ that contains
several instances of a Q2N2222 bipolar transistor.
Suppose also that you are interested in the effect of base
resistance variation on one specific device: Q6. To do this,
you need to do the following:
•
Define a tolerance (in this example, 5%) on the Rb
model parameter.
•
Set up and run a Monte Carlo analysis.
The following example demonstrates how to set up the
instance model for Q6.
Starting the Model Editor
To start the Model Editor, you need to:
1
In the schematic page editor, select Q6 on the
schematic page.
2
From the Edit menu, choose PSpice Model.
The Model Editor automatically creates a copy of the
Q2N2222 base model definition.
3
In the Model Editor, from the View menu, choose
Model Text.
The Model Editor displays the PSpice syntax for the
copied model in the text editing area.
Editing the Q2N2222-X model instance
To find out more about PSpice command
and netlist syntax, refer to the online
OrCA D PSpice A /D Reference
Manual.
114
Text edits appropriate to this example are as follows:
•
Add the DEV 5% clause to the Rb statement (required).
•
Change the model name to Q2N2222-MC (optional, for
descriptive purposes only).
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Using the Create Subcircuit command
Saving the edits and updating the schematic
When you choose Save from the File menu, two things
happen:
•
The Model Editor saves the model definition to the
model library.
•
The schematic page editor updates the
Implementation property value to Q2N2222-MC for
the Q6 part instance.
In this example, the default model library is MY.LIB. If
MY.LIB does not already exist, the Model Editor creates
and saves it in the current working directory. The
schematic page editor then automatically configures it as
a design model library for use with the current design
only.
If you verify the model library
configuration (in the Simulation Settings
dialog box, click the Libraries tab), you see
entries for NOM.LIB* (for global use, as
denoted by the asterisk) and MY.LIB (for
design use, no asterisk) in the Library files
list.
You can change the model reference for
this part back to the original Q2N2222 by
following the procedure To change
model references for part
instances on your design on
page 4-117.
Now you are ready to set up and run the Monte Carlo
analysis.
Using the Create Subcircuit
command
The Create Subcircuit command creates a subcircuit
netlist definition for the displayed level of hierarchy and
all lower levels in your design.
The schematic page editor does the following things for
you:
•
Maps any named interface ports at the active level of
hierarchy to terminal nodes in the PSpice .SUBCKT
statement.
•
Saves the subcircuit definition to a file named
DESIGN_NAME.SUB.
The Create Subcircuit command does not
help you create a hierarchical design. You
need to do this yourself before using the
Create Subcircuit command. For
information on hierarchical designs and
how to create them, refer to the OrCA D
Capture User’s Guide.
Before you can use the subcircuit definition in your
design, you need to:
•
Create a part for the subcircuit.
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Chapter 4 Creating and editing models
•
Configure the DESIGN_NAME.SUB file so PSpice
knows where to find it.
To create a subcircuit definition for a portion of your design
To create a part for the subcircuit
1
In the schematic page editor, move to the level of
hierarchy for which you want to create a subcircuit
(.SUBCKT) definition.
2
From the Place menu, choose Hierarchical Port.
3
From the File menu, choose Save.
4
In the Project Manager, from the Tools menu, choose
Create Netlist.
5
Select the PSpice tab.
6
In the Options frame, select Create SubCircuit Format
Netlist.
7
Click OK to generate the subcircuit definition and save
it to DESIGN_NAME.SUB.
To configure the subcircuit file
Refinements can include extending the
subcircuit definition using the optional
nodes construct, OPTIONAL:, the variable
parameters construct, PARAMS:, and the
.FUNC and local .PARAM commands.
1
In the schematic page editor, from the PSpice menu,
choose Edit Simulation Settings to display the
Simulation Settings dialog box.
2
Click either the Libraries tab or the Include Files tab,
then configure DESIGN_NAME.SUB as either a model
library or an include file (see Configuring model libraries
on page 4-120).
3
If necessary, refine the subcircuit definition for the
new part or for a part instance on your schematic page
using the Model Editor (see Editing model text on
page 4-110).
4
From Capture’s Edit menu, choose Part to start the
part editor.
5
Create a new part for the subcircuit definition.
One way to do this is to use the part wizard. See
Chapter 5, Creating parts for models for a complete
discussion.
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Changing the model reference to an existing model definition
Changing the model reference to
an existing model definition
Parts are linked to models by the model name assigned to
the parts’ Implementation property. You can change this
assignment by replacing the Implementation property
value with the name of a different model that already
exists in the library.
You can do this for:
•
A part instance in your design.
•
A part in the part library.
To change model references for part instances on your design
1
Find the name of the model that you want to use.
2
In the schematic page editor, select one or more parts
on your schematic page.
3
From the Edit menu, choose Properties.
The Parts spreadsheet appears.
4
Click the cell under the column Implementation Type.
5
From the Implementation list, select PSpice Model.
6
In the Implementation column, type the name of the
existing model that you want to use if it is not already
listed.
7
Click Apply to update the changes, then close the
spreadsheet.
To change the model reference for a part in the part library
1
Find the name of the model that you want to use.
2
In the schematic page editor, select the part you want
to change.
3
From the Edit menu, choose Part to start the part
editor with that part loaded for editing.
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Chapter 4 Creating and editing models
4
From the Options menu, choose Part Properties to
display the User Properties dialog box.
5
Select Implementation Type.
6
From the Implementation list, select PSpice Model.
7
In the Implementation text box, type the name of the
existing model that you want to use if it is not already
listed.
8
Click OK to close the Edit Part dialog box.
Reusing instance models
For information on how to create instance
models, see:
If you created instance models in your design and want to
reuse them, there are two things you can do:
• Running the Model Editor
•
Attach the instance model implementation to other
part instances in the same design.
•
Change the instance model to a global model and
create a part that corresponds to it.
from the
schematic page editor on
page 4-101.
• Starting the Model Editor
from the schematic page
editor in Capture on
page 4-111.
Reusing instance models in the same schematic
There are two ways to use the instance model elsewhere
in the same design.
To use the instance model elsewhere in your design
1
See Changing the model
reference to an existing model
definition on page 4-117.
118
Do one of the following:
•
Change the model reference for other part
instances to the name of the new model instance.
•
From the Edit menu, use the Copy and Paste
commands to place more part instances.
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Reusing instance models
Making instance models available to all designs
If you are refining model behavior specific to your design,
and are ready to make it available to any design, then you
need to link the model definition to a part and configure it
for global use.
To make your instance model available to any design
1
Create a part and assign the instance model name to
the Implementation property.
See Chapter 5, Creating parts for
models for more information.
2
If needed, move the instance model definition to an
appropriate model library, and make sure the library
is configured for global use.
See Configuring model libraries
on page 4-120 for more information.
Note
If you use the part wizard to create the part automatically from the
model definition, then this step is completed for you.
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Chapter 4 Creating and editing models
Configuring model libraries
Although model libraries are usually configured for you,
there are things that you sometimes must do yourself.
These are:
•
adding new model libraries that were created outside
of Capture or the Model Editor
•
changing the global or design scope of a model library
•
changing the library search order
•
changing or adding directory search paths
The Libraries and Include Files tabs
The Libraries and Include Files tabs of the Simulation
Settings dialog box are where you can add, change, and
remove model libraries and include files from the
configuration or resequence the search order.
Removing a library in this dialog box means that you are removing
the model library from the configured list. The library still exists on
your computer and you can add it back to the configuration later.
Note
To display the Libraries tab
The Include Files tab contains include files.
You can manually add design and global
include files to your configuration using the
Add to Design and Add as Global buttons,
respectively.
The Stimulus tab contains stimulus files. See
Configuring stimulus files on
page 10-254 for more information.
120
1
In PSpice, from the Simulation menu, choose Edit
Simulation Settings.
2
Click the Libraries tab.
The Library Files list shows the model libraries that
PSpice searches for definitions matching the parts in
your design. Files showing an asterisk ( * ) after their
name have global scope; files with names left
unmarked have design scope.
The buttons for adding model libraries to the
configuration follow the same local/global syntax
convention. Click one of the following:
•
Add to Design for design models.
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Configuring model libraries
•
Add as Global for global models.
Caution—When you use
include files instead
How PSpice uses model libraries
PSpice treats model library and include files
differently as follows:
PSpice searches libraries for any information it needs to
complete the definition of a part or to run a simulation. If
an up-to-date index does not already exist, PSpice
automatically generates an index file and uses the index to
access only the model definitions relevant to the
simulation. This means:
• For model library files, PSpice reads in
•
Disk space is not used up with definitions that your
design does not use.
•
There is no memory penalty for having large model
libraries.
•
Loading time is kept to a minimum.
Search order
When searching for model definitions, PSpice scans the
model libraries using these criteria:
•
design model libraries before global model libraries
•
model library sequence as listed in the Libraries tab of
the Simulation Settings dialog box
•
local directory (where the current design resides) first,
then the list of directories specified in the library
search path in the order given (see Changing the library
search path on page 4-125)
only the definitions it needs to run the
current simulation.
• For include files, PSpice reads in the file
in its entirety.
This means if you configure a model library
(*.LIB extension) as an include file using
the Add to Design or Add as Global button,
PSpice loads every model definition
contained in that file.
If the model library is large, you may
overload the memory capacity of your
system. However, when developing
models, you can do the following:
1 Initially configure the model library as
an include file; this avoids rebuilding
the index files every time the model
library changes.
2 When your models are stable,
reconfigure the include file containing
the model definitions as a library file.
To reconfigure an include file as a library
file:
1 From the Simulation menu, choose Edit
Simulation Settings, then click the
Include Files tab.
2 Select the include file that you want to
change.
3 Click either the Add as Global or the
Add to Design button.
4 Click Remove to remove the include file
entry.
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Chapter 4 Creating and editing models
Handling duplicate model names
If your model libraries contain duplicate model names,
PSpice always uses the first model it finds. This means
you might need to resequence the search order to make
sure PSpice uses the model that you want. See Changing
model library search order on page 4-124.
PSpice searches design libraries before global libraries, so if the
new model you want to use is specific to your design and the
duplicate definition is global, you do not need to make any
changes.
Note
Adding model libraries to the configuration
New libraries are added above the selected library name
in the Library Files list box.
To add model libraries to the configuration
1
From the Simulation menu, choose Edit Simulation
Settings, then click the Libraries tab.
2
Click the library name positioned one entry below
where you want to add the new library.
3
In the Filename text box, either:
4
5
122
•
type the name of the model library, or
•
click Browse to locate and select the library.
Do one of the following:
•
If the model definitions are for use in the current
design only, click the Add to Design button.
•
If the model definitions are for global use in any
schematic, click the Add as Global button instead.
Click OK.
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Configuring model libraries
If the model libraries reside in a directory that is not on the library
search path, and you use the Browse button in step 3 to select the
libraries you want to add, then the schematic editor automatically
updates the library search path. Otherwise, you need to add the
directory path yourself. See Changing the library search path
on page 4-125.
Note
Changing design and global scope
There are times when you might need to change the scope
of a model library from design to global, or vice versa.
To change the scope of a design model to global
1
From the Simulation menu, choose Edit Simulation
Settings, then click the Libraries tab.
2
Select the model library that you want to change.
3
Do one of the following:
4
•
Click the Add as Global button to add a global
entry.
•
Click the Add to Design button to add a design
entry.
Example: If you have an instance model
that you now want to make available to
any design, then you need to change the
local model library that contains it to have
global scope.
For more information, see Global vs.
design models and libraries on
page 4-89.
Click the Delete toolbar button to remove the local
entry.
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Chapter 4 Creating and editing models
Changing model library search order
Two reasons why you might want to change the search
order are to:
See Handling duplicate model
names on page 4-122 for more
information.
•
reduce the search time
•
avoid using the wrong model when there are model
names duplicated across libraries; PSpice always uses
the first instance
To change the order of libraries
1
2
Caution—Do not edit NOM.LIB. If you
do, PSpice will recreate the indexes for
every model library referenced in
NOM.LIB. This can take some time.
124
On the Libraries tab of the Simulation Settings dialog
box:
a
Select the library name you wish to move.
b
Use either the Up Arrow or Down Arrow toolbar
button to move the library name to a different
place in the list.
If you have listed multiple *.LIB commands within a
single library (like NOM.LIB), then edit the library
using a text editor to change the order.
Example: The model libraries DIODES.LIB and
EDIODES.LIB (European manufactured diodes) shipped
with your OrCAD programs have identically named
device definitions. If your design uses a device out of one
of these libraries, you need to position the model library
containing the definition of choice earlier in the list. If
your system is configured as originally shipped, this
means you need to add the specific library to the list before
NOM.LIB.
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Configuring model libraries
Changing the library search path
For model libraries that are configured without explicit
path names, PSpice first searches the directory where the
current design resides, then steps down the list of
directories specified in the Library Path text box on the
Libraries tab of the Simulation Settings dialog box.
To change the library search path
1
From the Simulation menu, choose Edit Simulation
Settings to display the Simulation Settings dialog box.
2
Click the Libraries tab.
3
In the Library Path text box, position the pointer after
the directory path that PSpice should search before the
new path.
4
Type in the new path name following these rules:
•
Use a semi-colon character ( ; ) to separate two
path names.
•
Do not follow the last path name with a
semi-colon.
Example: To search first
C:\ORCAD\LIB, then
C:\MYLIBS, for model libraries, type
"C:\ORCAD\LIB";"C:\MYLIBS"
in the Library Path text box.
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Chapter 4 Creating and editing models
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Creating parts for models
5
Chapter overview
This chapter provides information about creating parts for
model definitions, so you can simulate the model from
your design using OrCAD Capture.
Topics are grouped into four areas introduced later in this
overview. If you want to find out quickly which tools to
use to complete a given task and how to start, then:
1
Go to the roadmap in Ways to create parts for models on
page 5-129.
2
Find the task you want to complete.
3
Go to the sections referenced for that task for more
information about how to proceed.
For general information about creating
parts, refer to the OrCA D Capture
User’s Guide.
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Chapter 5 Creating parts for models
Background information
These sections provide
background on the things you need to know and do to
prepare for creating parts:
•
What’s different about parts used for simulation? on
page 5-129
•
Preparing your models for part creation on page 5-130
Task roadmap This section helps you find the sections
in this chapter that are relevant to the part creation task
that you want to complete:
•
Ways to create parts for models on page 5-129
How to use the tools These sections explain how to
use different tools to create parts for model definitions:
•
Using the Model Editor to create parts on page 5-131
•
Using the Model Editor to create parts on page 5-131
•
Basing new parts on a custom set of parts on page 5-133
Other useful information
These sections explain
how to refine part graphics and properties:
128
•
Editing part graphics on page 5-135
•
Defining part properties needed for simulation on
page 5-139
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What’s different about parts used for simulation?
What’s different about parts
used for simulation?
A part used for simulation has these special
characteristics:
•
a link to a simulation model
•
a netlist translation
•
modeled pins
For information on adding simulation
models to a model library, see Chapter
4, Creating and editing models.
Ways to create parts
for models
If you want to...
Then do this...
To find out more, see this...
➥ Create parts for a set of
Use the Model Editor to
create parts from a model
library.
Basing new parts on a custom set
of parts on page 5-133
Use the Model Editor* and
enable automatic creation
of parts.
Using the Model Editor to create
parts on page 5-131
Using the Model Editor to edit
models on page 4-93
Basing new parts on a custom set
of parts on page 5-133
vendor or user-defined
models saved in a model
library.
➥ Change the graphic
standard for an existing
model library.
➥ Automatically create
one part each time you
extract a new model.
* For a list of device types that the Model Editor supports, see Model Editor-supported
device types on page 4-95.
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Chapter 5 Creating parts for models
Preparing your models for part
creation
If you already have model definitions and want to create
parts for them, you should organize the definitions into
libraries containing similar device types.
To set up a model library for part creation
1
Model libraries typically have a .LIB
extension. However, you can use a
different file extension as long as the file
format conforms to the standard model
library file format.
2
If all of your models are in one file and you wish to
keep them that way, rename the file to:
•
Reflect the kinds of models contained in the file.
•
Have the .LIB extension.
If each model is in its own file, and you want to
concatenate them into one file, use the DOS copy
command.
Example: You can append a set of files with .MOD
extensions into a single .LIB file using the DOS
command:
copy *.MOD MYLIB.LIB
For information on managing model
libraries, including the search order PSpice
uses, see Configuring model
libraries on page 4-120.
130
3
Make sure the model names in your new library do
not conflict with model names in any other model
library.
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Using the Model Editor to create parts
Using the Model Editor to create
parts
If you want to run the Model Editor and enable automatic
creation of parts for any model that you create or change,
then run the Model Editor alone. This means any models
you create are not tied to the current design or to a part
editing session.
Note
If you open an existing model library, the Model Editor creates
parts for only the models that you change or add to it.
To find out how to use the Model Editor to
create models, see Using the Model
Editor to edit models on
page 4-93.
To find out which device types the Model
Editor supports, see Model
Editor-supported device types on
page 4-95.
Starting the Model Editor
To start the Model Editor alone
1
From the Windows Start menu, point to the OrCAD
Release 9 program folder, then choose PSpice Model
Editor.
2
From the File menu, choose Open or New, and enter
an existing or new model library name.
3
In the Models List frame, select the name of a model to
display it for editing in the Spec Entry frame.
To start the Model Editor from within Capture
1
In the schematic page editor, select the part whose
model you want to edit.
2
From the Edit menu, choose PSpice Model.
The Model Editor starts with the model loaded for
editing.
If you have already started the Model
Editor from Capture, and want to continue
working on new models and parts, then:
1 Close the opened model library.
2 Open a new model library.
3 Load a device model or create a new
one.
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Chapter 5 Creating parts for models
Setting up automatic part creation
Part creation from the Model Editor is optional. By
default, automatic part creation is enabled. However, if
you previously disabled part creation, you need to enable
it before creating a new model and part.
Instead of using the OrCAD default part set,
you can use your own set of standard parts.
To find out more, see Basing new
parts on a custom set of parts on
page 5-133.
For example, if the model library is named
MYPARTS.LIB, then the Model Editor creates
the part library named MYPARTS.OLB.
132
To automatically create parts for new models
1
In the Model Editor, from the Tools menu, choose
Options.
2
In the Part Creation Setup frame, select Create Parts
for Models if it is not already enabled.
3
In the Save Part To frame, define the name of the part
library for the new part. Choose one of the following:
•
Part library path same as model library to create or
open the *.OLB file that has the same filename as
the open model library (*.LIB).
•
User-defined part library, and then enter a library
name in the part Library Name text box.
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Basing new parts on a custom set of parts
Basing new parts on a custom
set of parts
If you are using the the Model Editor to automatically
generate parts for model definitions, and you want to base
the new parts on a custom graphic standard (rather than
the OrCAD default parts), then you can change which
underlying parts either application uses by setting up
your own set of parts.
Note If you use a custom part set, the
Model Editor always checks the custom part
library first for a part that matches the
model definition. If none can be found,
they use the OrCAD default part instead.
To create a custom set of parts for automatic part generation
1
Create a part library with the custom parts.
Be sure to name these parts by their device type as
shown in Table 2; this is how the Model Editor
determines which part to use for a model definition.
Table 2
For more information on creating parts,
refer to the OrCA D Capture User’s
Guide.
Part names for custom part generation.
For this device type...
Use this part name...
For this device type...
Use this part name...
Bipolar transistor: LPNP
LPNP
MOSFET: N-channel
NMOS
Bipolar transistor: NPN
NPN
MOSFET: P-channel
PMOS
Bipolar transistor: PNP
PNP
OPAMP: 5-pin
OPAMP5
Capacitor*
CAP
OPAMP: 7-pin
OPAMP7
Diode
DIODE
Resistor*
RES
GaAsFET*
GASFET
Switch: voltage-controlled*
VSWITCH
IGBT: N-channel
NIGBT
Transmission line*
TRN
Inductor*
IND
Voltage comparator
VCOMP
JFET: N-channel
NJF
Voltage comparator: 6 pin
VCOMP6
JFET: P-channel
PJF
Voltage reference
VREF
Magnetic core
CORE
Voltage regulator
VREG
* Does not apply to the Model Editor.
2
For each custom part, set its MODEL property to `M
where ` is a back-single quote or grave character.
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Chapter 5 Creating parts for models
This tells the Model Editor to substitute the correct
model name.
To base new parts on custom parts using the Model Editor
134
1
In the Model Editor, from the Options menu, choose
Part Creation Setup, and enable automatic part
creation as described in To automatically create parts for
new models on page 5-132.
2
In the Base Parts On frame, enter the name of the
existing part library (*.OLB) that contains your custom
parts.
3
Click OK.
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Editing part graphics
Editing part graphics
If you created parts using the Model Editor, and you want
to make further changes, the following sections explain a
few important things to remember when you edit the
parts.
When changing part graphics, check to see
that all pins are on the grid.
How Capture places parts
When placing parts on the schematic page, the schematic
page editor uses the grid as a point of reference for
different editing activities. The part’s pin ends are
positioned on the grid points.
grid point
part body border
To edit a part in a library
1
From Capture’s File menu, point to Open, then choose
Library.
2
Select the library that has the part you want to edit.
The library opens and displays all its parts.
3
Double-click the part you want to edit.
The part appears in the part editor.
4
Edit the part.
You can resize it, add or delete graphics, and add or
delete pins.
For more information about specific part
editing tasks, refer to the OrCA D
Capture User’s Guide.
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Chapter 5 Creating parts for models
5
After you have finished editing the part, from the File
menu, choose Save to save the part to its library.
Defining grid spacing
Grid spacing for graphics
The grid, denoted by evenly spaced grid points, regulates
the sizing and positioning of graphic objects and the
positioning of pins. The default grid spacing with
snap-to-grid enabled is 0.10", and the grid spacing is 0.01".
You can turn off the grid spacing when you need to draw
graphics in a tighter space.
To edit the part graphics
Note Pin changes that alter the part
template can occur if you either:
• change pin names
1
In Capture’s part editor, display the part you want to
edit.
2
Select the line, arc, circle, or other graphic object you
want to change, and do any of the following:
•
To stretch or shrink the graphic object, click and
drag one of the size handles.
•
To move the entire part graphic, click and drag the
edge of the part.
The part body border automatically changes to fit
the size of the part graphic.
3
After you have finished editing the part, from the File
menu, choose Save to save the part to its library.
or
• delete pins
Grid spacing for pins
In these cases you must adjust the value of
the part’s PSPICETEMPLATE property to
reflect these changes. To find out how, see
Pin callout in subcircuit
templates on page 5-144.
The part editor always places pins on the grid, even when
the snap-to-grid option is turned off. The size of the part is
relative to the pin-to-pin spacing for that part. That means
that pins placed one grid space apart in the part editor are
displayed as one grid space apart in the schematic page
editor.
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Editing part graphics
Pins must be placed on the grid at integer multiples of the
grid spacing. Because the default grid spacing for the
Schematic Page Grid is set at 0.10", OrCAD recommends
setting pin spacing in the Part and Symbol Grid at 0.10"
intervals from the origin of the part and at least 0.10" from
any adjacent pins.
The part editor considers pins that are not placed at
integer multiples of the grid spacing from the origin as
off-grid, and a warning appears when you try to save the
part.
For more information about grid spacing
and pin placement, refer to the OrCA D
Capture User’s Guide.
Here are two guidelines:
•
Make sure Pointer Snap to Grid is enabled when
editing part pins and editing schematic pages so you
can easily make connections.
•
Make sure the Part and Symbol Grid spacing matches
the Schematic Page Grid spacing.
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Chapter 5 Creating parts for models
Attaching models to parts
If you create parts and want to simulate them, you need to
attach model implementations to them. If you created
your parts using any of the methods discussed in this
chapter, then your part will have a model implementation
already attached to it.
MODEL
The Implementation property defines the name of the
model that PSpice must use for simulation. When
attaching this implementation, this rule applies:
•
The Implementation name should match the name of
the .MODEL or .SUBCKT definition of the simulation
model as it appears in the model library (*.LIB).
Example: If your design includes a 2N2222 bipolar
transistor with a .MODEL name of Q2N2222, then the
Implementation name for that part should be Q2N2222.
Note
For more information on model editing in
general, see Chapter 4, Creating
and editing models. For specific
information on changing model references,
see Changing the model reference
to an existing model definition
on page 4-117.
You do not need to enter an
Implementation Path because PSpice
searches for the model in the list of model
libraries you configure for this project.
138
Make sure that the model library containing the definition for the
attached model is configured in the list of libraries for your project.
See Configuring model libraries on page 4-120 for more
information.
To attach a model implementation
1
In the schematic page editor, double-click a part to
display the Parts spreadsheet of the Property Editor.
2
From the Implementation list, select PSpice Model.
3
In the Implementation column, type the name of the
model to attach to the part.
4
Click Apply to update the design, then close the Parts
spreadsheet.
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Defining part properties needed for simulation
Defining part properties needed
for simulation
If you created your parts using any of the methods
discussed in this chapter, then your part will have these
properties already defined for it:
•
PSpice PSPICETEMPLATE for simulation
•
PART and REFDES for identification
For example, if you create a part that has electrical
behavior described by the subcircuit definition that starts
with:
Here are the things to check when editing
part properties:
✔ Does the PSPICETEMPLATE specify the
correct number of pins/nodes?
✔ Are the pins/nodes in the
PSPICETEMPLATE specified in the
proper order?
✔ Do the pin/node names in the
PSPICETEMPLATE match the pin names
on the part?
.SUBCKT 7400 A B Y
+ optional: DPWR=$G_DPWR DGND=$G_DGND
+ params: MNTYMXDLY=0 IO_LEVEL=0
To edit a property needed for simulation:
then the appropriate part properties are:
IMPLEMENTATION = 7400
MNTYMXDLY = 0
IO_LEVEL = 0
PSPICETEMPLATE = X^@REFDES %A %B %Y %PWR
%GND
@MODEL PARAMS:[email protected]_LEVEL
[email protected]
Note
For clarity, the PSPICETEMPLATE property value is shown here in
multiple lines; in a part definition, it is specified in one line (no line
breaks).
Table 3
To find out more about this property...
See this...
PSPICETEMPLATE
page 5-140
1 In the schematic page editor, select the
part to edit.
2 From the Edit menu, choose Properties
to display the Parts spreadsheet of the
Property Editor.
3 Click in the cell of the column you want
to change (for example,
PSPICETEMPLATE), or click the New
button to add a property (and type the
property name in the Name text box).
4 If needed, type a value in the Value
text box.
5 Click Apply to update the design, then
close the spreadsheet.
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Chapter 5 Creating parts for models
PSPICETEMPLATE
Caution—Creating parts
not intended for simulation
Some part libraries contain parts designed
only for board layout; PSpice cannot
simulate these parts. This means they do
not have PSPICETEMPLATE properties or
that the PSPICETEMPLATE property value is
blank.
The PSPICETEMPLATE property defines the PSpice
syntax for the part’s netlist entry. When creating a netlist,
Capture substitutes actual values from the circuit into the
appropriate places in the PSPICETEMPLATE syntax, then
saves the translated statement to the netlist file.
Any part that you want to simulate must have a defined
PSPICETEMPLATE property. These rules apply:
•
The pin names specified in the PSPICETEMPLATE
property must match the pin names on the part.
•
The number and order of the pins listed in the
PSPICETEMPLATE property must match those for
the associated .MODEL or .SUBCKT definition
referenced for simulation.
•
The first character in a PSPICETEMPLATE must be a
PSpice device letter appropriate for the part (such as Q
for a bipolar transistor).
PSPICETEMPLATE syntax
The PSPICETEMPLATE contains:
•
regular characters that the schematic page editor
interprets verbatim
•
property names and control characters that the schematic
page editor translates
Regular characters in templates
Regular characters include the following:
•
alphanumerics
•
any keyboard part except the special syntactical parts
used with properties (@ & ? ~ #).
•
white space
An identifier is a collection of regular characters of the
form:
alphabetic character [any other regular character]*.
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Defining part properties needed for simulation
Property names in templates
Property names are preceded by a special character as
follows:
[ @ | ? | ~ | # | & ]<identifier>
The schematic page editor processes the property
according to the special character as shown in the
following table.
Table 4
This syntax...*
Is replaced with this...
@<id>
Value of <id>. Error if no <id> attribute or
if no value assigned.
&<id>
Value of <id> if <id> is defined.
?<id>s...s
Text between s...s separators if <id> is
defined.
?<id>s...ss...s
Text between the first s...s separators if
<id> is defined, else the second s...s clause.
~<id>s...s
Text between s...s separators if <id> is
undefined.
~<id> s...ss...s
Text between the first s...s separators if
<id> is undefined, else the second s...s
clause.
#<id>s...s
Text between s...s separators if <id> is
defined, but delete rest of template if <id>
is undefined.
* s is a separator character
Separator characters include commas (,), periods (.),
semi-colons (;), forward slashes (/), and vertical
bars ( | ). You must always use the same character to
specify an opening-closing pair of separators.
Note
You can use different separator characters to nest conditional
property clauses.
Example: The template fragment
?G|[email protected]||G=1000| uses the vertical
bar as the separator between the
if-then-else parts of this conditional clause.
If G has a value, then this fragment
translates to G=<G property value>.
Otherwise, this fragment translates to
G=1000.
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Chapter 5 Creating parts for models
Caution—Recommended
scheme for netlist
templates
Templates for devices in the part library
start with a PSpice device letter, followed
by the hierarchical path, and then the
reference designator (REFDES) property.
OrCAD recommends that you adopt this
scheme when defining your own netlist
templates.
Example: R^@REFDES ... for a resistor
The ^ character in templates
The schematic page editor replaces the ^ character with
the complete hierarchical path to the device being
netlisted.
The \n character sequence in templates
The part editor replaces the character sequence \n with a
new line. Using \n, you can specify a multi-line netlist
entry from a one-line template.
The % character and pin names in templates
Pin names are denoted as follows:
%<pin name>
where pin name is one or more regular characters.
The schematic page editor replaces the %<pin name>
clause in the template with the name of the net connected
to that pin.
The end of the pin name is marked with a separator (see
Property names in templates on page 5-141). To avoid name
conflicts in PSpice, the schematic page editor translates
the following characters contained in pin names.
Table 5
This pin name character... Is replaced with this...
<
l (L)
>
g
=
e
\XXX\
XXXbar
Note
142
To include a literal % character in the netlist, type %% in the
template.
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Defining part properties needed for simulation
PSPICETEMPLATE examples
Simple resistor (R) template
The R part has:
•
two pins: 1 and 2
•
two required properties: REFDES and VALUE
Template
R^@REFDES %1 %2 @VALUE
Sample translation
R_R23 abc def 1k
where REFDES equals R23, VALUE equals 1k, and R
is connected to nets abc and def.
Voltage source with optional AC and DC specifications (VAC)
template
The VAC part has:
•
two properties: AC and DC
•
two pins: + and -
Template
V^@REFDES %+ %- ?DC|[email protected]| ?AC|[email protected]|
Sample translation
V_V6 vp vm DC=5v
where REFDES equals V6, VSRC is connected to nodes
vp and vm, DC is set to 5v, and AC is undefined.
Sample translation
V_V6 vp vm DC=5v AC=1v
where, in addition to the settings for the previous
translation, AC is set to 1v.
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Chapter 5 Creating parts for models
Parameterized subcircuit call (X) template
Suppose you have a subcircuit Z that has:
•
two pins: a and b
•
a subcircuit parameter: G, where G defaults to 1000
when no value is supplied
To allow the parameter to be changed on the schematic
page, treat G as an property in the template.
Note For clarity, the PSPICETEMPLATE
property value is shown here in multiple
lines; in a part definition, it is specified in
one line (no line breaks).
Template
X^@REFDES %a %b Z PARAMS: ?G|[email protected]|
~G|G=1000|
Equivalent template (using the if...else form)
X^@REFDES %a %b Z PARAMS: ?G|[email protected]||G=1000|
Sample translation
X_U33 101 102 Z PARAMS: G=1024
where REFDES equals U33, G is set to 1024, and the
subcircuit connects to nets 101 and 102.
Sample translation
X_U33 101 102 Z PARAMS: G=1000
where the settings of the previous translation apply
except that G is undefined.
Pin callout in subcircuit templates
To find out how to define subcircuits, refer
to the .SUBCKT command in the online
OrCA D PSpice A /D Reference
Manual.
The number and sequence of pins named in a template for
a subcircuit must agree with the definition of the
subcircuit itself—that is, the node names listed in the
.SUBCKT statement, which heads the definition of a
subcircuit. These are the pinouts of the subcircuit.
Example: Consider the following first line of a
(hypothetical) subcircuit definition:
.SUBCKT SAMPLE 10 3 27 2
The four numbers following the name SAMPLE—10, 3,
27, and 2—are the node names for this subcircuit’s
pinouts.
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Defining part properties needed for simulation
Now suppose that the part definition shows four pins:
IN+
T-
OUT+
IN-
OU
The number of pins on the part equals the number of
nodes in the subcircuit definition.
If the correspondence between pin names and nodes is as
follows:
Table 6
This node name...
Corresponds to this pin name...
10
IN+
3
IN-
27
OUT+
2
OUT-
then the template looks like this:
X^@REFDES %IN+ %IN- %OUT+ %OUT- @MODEL
The rules of agreement are outlined in Figure 34.
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Chapter 5 Creating parts for models
Number of nodes in first line
of subcircuit definition
Sequence of nodes in first line
of subcircuit definition
must equal
Number of pins called out
in template
must equal Number of modeled* pins
shown in part
must match Sequence of pins called out
in template
Names of pins called out
in template
must match Names of modeled* pins
shown in part
* Unmodeled pins may appear on a part (like the two voltage offset pins on a 741 opamp part).
These pins are not netlisted and do not appear on the template.
Figure 34 Rules for pin callout in subcircuit templates.
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Analog behavioral modeling
6
Chapter overview
This chapter describes how to use the Analog Behavioral
Modeling (ABM) feature of PSpice. This chapter includes
the following sections:
•
Overview of analog behavioral modeling on page 6-148
•
The ABM.OLB part library file on page 6-149
•
Placing and specifying ABM parts on page 6-150
•
ABM part templates on page 6-152
•
Control system parts on page 6-153
•
PSpice-equivalent parts on page 6-174
•
Cautions and recommendations for simulation and analysis
on page 6-186
•
Basic controlled sources on page 6-192
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Chapter 6 Analog behavioral modeling
Overview of analog behavioral
modeling
You can use the Analog Behavioral Modeling (ABM)
feature of PSpice to make flexible descriptions of
electronic components in terms of a transfer function or
lookup table. In other words, a mathematical relationship
is used to model a circuit segment, so you do not need to
design the segment component by component.
The part library contains several ABM parts that are
classified as either control system parts or as
PSpice-equivalent parts. See Basic controlled sources on
page 6-192 for an introduction to these parts, how to use
them, and the difference between parts with
general-purpose application and parts with
special-purpose application.
Control system parts are defined with the reference
voltage preset to ground so that each controlling input
and output are represented by a single pin in the part.
These are described in Control system parts on page 6-153.
PSpice-equivalent parts reflect the structure of the PSpice
E and G device types, which respond to a differential
input and have double-ended output. These are described
in PSpice-equivalent parts on page 6-174.
You can also use the Device Equations option (described
in the online OrCA D PSpice A /D Reference Manual) for
modeling of this type, but OrCAD recommends using the
ABM feature wherever possible. With Device Equations,
the PSpice source code is actually modified. While this is
more flexible and produces faster results, it is also much
more difficult to use and to troubleshoot. Also, any
changes you make using Device Equations must be made
to all new PSpice updates you install.
Device models made with ABM can be used for most
cases, are much easier to create, and are compatible with
PSpice updates.
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The ABM.OLB part library file
The ABM.OLB part library file
The part library ABM.OLB contains the ABM
components. This library contains two sections.
The first section has parts that you can quickly connect to
form control system types of circuits. These components
have names like SUM, GAIN, LAPLACE, and HIPASS.
The second section contains parts that are useful for more
traditional controlled source forms of schematic parts.
These PSpice-equivalent parts have names like EVALUE
and GFREQ and are based on extensions to traditional
PSpice E and G device types.
Implement ABM components by using PSpice primitives;
there is no corresponding abm.lib model library. A few
components generate multi-line netlist entries, but most
are implemented as single PSpice E or G device
declarations. See ABM part templates on page 6-152 for a
description of PSPICETEMPLATE properties and their
role in generating netlist declarations. See Implementation
of PSpice -equivalent parts on page 6-175 for more
information about PSpice E and G syntax.
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Chapter 6 Analog behavioral modeling
Placing and specifying ABM
parts
Place and connect ABM parts the same way you place
other parts. After you place an ABM part, you can edit the
instance properties to customize the operational behavior
of the part. This is equivalent to defining an ABM
expression describing how inputs are transformed into
outputs. The following sections describe the rules for
specifying ABM expressions.
Net names and device names in ABM expressions
In ABM expressions, refer to signals by name. This is also
considerably more convenient than having to connect a
wire from a pin on an ABM component to a point carrying
the voltage of interest.
The name of an interface port does not
extend to any connected nets. To refer to a
signal originating at an interface port,
connect the port to an offpage connector of
the desired name.
If you used an expression such as V(2), then the referenced
net (2 in this case) is interpreted as the name of a local or
global net. A local net is a labeled wire or bus segment in
a hierarchical schematic, or a labeled offpage connector. A
global net is a labeled wire or bus segment at the top level,
or a global connector.
OrCAD Capture recognizes these constructs in ABM
expressions:
V(<net name>)
V(<net name>,<net name>)
I(<vdevice>)
When one of these is recognized, Capture searches for
<net name> or <vdevice> in the net name space or the
device name space, respectively. Names are searched for
first at the hierarchical level of the part being netlisted. If
not found there, then the set of global names is searched.
If the fragment is not found, then a warning is issued but
Capture still outputs the resulting netlist. When a match is
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Placing and specifying ABM parts
found, the original fragment is replaced by the fully
qualified name of the net or device.
For example, suppose we have a hierarchical part U1.
Inside the schematic representing U1 we have an ABM
expression including the term V(Reference). If
“Reference” is the name of a local net, then the fragment
written to the netlist will be translated to
V(U1_Reference). If “Reference” is the name of a global
net, the corresponding netlist fragment will be
V(Reference).
Names of voltage sources are treated similarly. For
example, an expression including the term I(Vsense) will
be output as I(V_U1_Vsense) if the voltage source exists
locally, and as I(V_Vsense) if the voltage source exists at
the top level.
Forcing the use of a global definition
If a net name exists both at the local hierarchical level and
at the top level, the search mechanism used by Capture
will find the local definition. You can override this, and
force Capture to use the global definition, by prefixing the
name with a single quote (') character.
For example, suppose there is a net called Reference both
inside hierarchical part U1 and at the top level. Then, the
ABM fragment V(Reference) will result in
V(U1_Reference) in the netlist, while the fragment
V('Reference) will produce V(Reference).
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Chapter 6 Analog behavioral modeling
ABM part templates
For most ABM parts, a single PSpice “E” or “G” device
declaration is output to the netlist per part instance. The
PSPICETEMPLATE property in these cases is
straightforward. For example the LOG part defines an
expression variant of the E device with its output being
the natural logarithm of the voltage between the input pin
and ground:
E^@REFDES %out 0 VALUE { LOG(V(%in)) }
The fragment E^@REFDES is standard. The “E” specifies
a PSpice controlled voltage source (E device); %in and
%out are the input and output pins, respectively; VALUE
is the keyword specifying the type of ABM device; and the
expression inside the curly braces defines the logarithm of
the input voltage.
Several ABM parts produce more than one primitive
PSpice device per part instance. In this case, the
PSPICETEMPLATE property may be quite complicated.
An example is the DIFFER (differentiator) part. This is
implemented as a capacitor in series with a current sensor
together with an E device which outputs a voltage
proportional to the current through the capacitor.
The template has several unusual features: it gives rise to
three primitives in the PSpice netlist, and it creates a local
node for the connection of the capacitor and its
current-sensing V device.
For clarity, the template is shown on three
lines although the actual template is a
single line.
C^@REFDES %in $$U^@REFDES 1\n
V^@REFDES $$U^@REFDES 0 0v\n
E^@REFDES %out 0 VALUE {@GAIN * I(V^@REFDES)}
The fragments C^@REFDES, V^@REFDES, and
E^@REFDES create a uniquely named capacitor, current
sensing V device, and E device, respectively. The
fragment $$U^@REFDES creates a name suitable for use
as a local node. The E device generates an output
proportional to the current through the local V device.
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Control system parts
Control system parts
Control system parts have single-pin inputs and outputs.
The reference for input and output voltages is analog
ground (0). An enhancement to PSpice means these
components can be connected together with no need for
dummy load or input resistors.
Table 7 lists the control system parts, grouped by
function. Also listed are characteristic properties that may
be set. In the sections that follow, each part and its
properties are described in more detail.
Table 7
Control system parts
Category
Part
Description
Properties
Basic
components
CONST
constant
VALUE
SUM
adder
MULT
multiplier
GAIN
gain block
DIFF
subtracter
LIMIT
hard limiter
LO, HI
GLIMIT
limiter with gain
LO, HI, GAIN
SOFTLIM
soft (tanh) limiter LO, HI, GAIN
LOPASS
lowpass filter
FP, FS, RIPPLE,
STOP
HIPASS
highpass filter
FP, FS, RIPPLE,
STOP
Limiters
Chebyshev
filters
GAIN
BANDPASS bandpass filter
F0, F1, F2, F3,
RIPPLE, STOP
BANDREJ
band reject
(notch) filter
F0, F1, F2, F3,
RIPPLE, STOP
Integrator and
differentiator
INTEG
integrator
GAIN, IC
DIFFER
differentiator
GAIN
Table look-ups
TABLE
lookup table
ROW1...ROW5
FTABLE
frequency lookup ROW1...ROW5
table
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Chapter 6 Analog behavioral modeling
Table 7
Control system parts (continued)
Category
Part
Description
Properties
Laplace
transform
LAPLACE
Laplace
expression
NUM, DENOM
Math functions
(where ‘x’ is the
input)
ABS
|x|
SQRT
x1/2
PWR
|x|EXP
EXP
PWRS
xEXP
EXP
LOG
ln(x)
LOG10
log(x)
EXP
ex
SIN
sin(x)
COS
cos(x)
TAN
tan(x)
ATAN
tan-1 (x)
ARCTAN
tan-1 (x)
ABM
no inputs, V out
EXP1...EXP4
ABM1
1 input, V out
EXP1...EXP4
ABM2
2 inputs, V out
EXP1...EXP4
ABM3
3 inputs, V out
EXP1...EXP4
ABM/I
no input, I out
EXP1...EXP4
ABM1/I
1 input, I out
EXP1...EXP4
ABM2/I
2 inputs, I out
EXP1...EXP4
ABM3/I
3 inputs, I out
EXP1...EXP4
Expression
functions
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Control system parts
Basic components
The basic components provide fundamental functions
and in many cases, do not require specifying property
values. These parts are described below.
CONST
VALUE
constant value
The CONST part outputs the voltage specified by the
VALUE property. This part provides no inputs and one
output.
SUM
The SUM part evaluates the voltages of the two input
sources, adds the two inputs together, then outputs the
sum. This part provides two inputs and one output.
MULT
The MULT part evaluates the voltages of the two input
sources, multiplies the two together, then outputs the
product. This part provides two inputs and one output.
GAIN
GAIN
constant gain value
The GAIN part multiplies the input by the constant
specified by the GAIN property, then outputs the result.
This part provides one input and one output.
DIFF
The DIFF part evaluates the voltage difference between
two inputs, then outputs the result. This part provides two
inputs and one output.
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Chapter 6 Analog behavioral modeling
Limiters
The Limiters can be used to restrict an output to values
between a set of specified ranges. These parts are
described below.
LIMIT
HI
upper limit value
LO
lower limit value
The LIMIT part constrains the output voltage to a value
between an upper limit (set with the HI property) and a
lower limit (set with the LO property). This part takes one
input and provides one output.
GLIMIT
HI
upper limit value
LO
lower limit value
GAIN
constant gain value
The GLIMIT part functions as a one-line opamp. The gain
is applied to the input voltage, then the output is
constrained to the limits set by the LO and HI properties.
This part takes one input and provides one output.
SOFTLIMIT
HI
upper limit value
LO
lower limit value
GAIN
constant gain value
A, B, V,
TANH
internal variables used to define the
limiting function
The SOFTLIMIT part provides a limiting function much
like the LIMIT device, except that it uses a continuous
curve limiting function, rather than a discontinuous
limiting function. This part takes one input and provides
one output.
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Control system parts
Chebyshev filters
The Chebyshev filters allow filtering of the signal based
on a set of frequency characteristics. The output of a
Chebyshev filter depends upon the analysis being
performed.
PSpice computes the impulse response of each Chebyshev filter
used in a transient analysis during circuit read-in. This may require
considerable computing time. A message is displayed on your
screen indicating that the computation is in progress.
Note
For DC and bias point, the output is simply the DC
response of the filter. For AC analysis, the output for each
frequency is the filter response at that frequency. For
transient analysis, the output is then the convolution of
the past values of the input with the impulse response of
the filter. These rules follow the standard method of using
Fourier transforms.
To obtain a listing of the filter Laplace coefficients for each stage,
choose Setup from the Analysis menu, click on Options, and enable
LIST in the Options dialog box.
Note
OrCAD Capture recommends looking at one
or more of the references cited in
Frequency-domain device
models on page 6-181, as well as
some of the following references on analog
filter design:
1 Ghavsi, M.S. & Laker, K.R., Modern
Filter Design, Prentice-Hall, 1981.
2 Gregorian, R. & Temes, G., Analog
MOS Integrated Circuits,
Wiley-Interscience, 1986.
3 Johnson, David E., Introduction to
Filter Theory, Prentice-Hall, 1976.
4 Lindquist, Claude S., Active Network
Design with Signal Filtering
Applications, Steward & Sons, 1977.
5 Stephenson, F.W. (ed), RC Active Filter
Design Handbook, Wiley, 1985.
Each of the Chebyshev filter parts is described in the
following pages.
6 Van Valkenburg, M.E., Analog Filter
Design, Holt, Rinehart & Winston,
1982.
LOPASS
7 Williams, A.B., Electronic Filter Design
Handbook, McGraw-Hill, 1981.
FS
stop band frequency
FP
pass band frequency
RIPPLE
pass band ripple in dB
STOP
stop band attenuation in dB
The LOPASS part is characterized by two cutoff
frequencies that delineate the boundaries of the filter pass
band and stop band. The attenuation values, RIPPLE and
STOP, define the maximum allowable attenuation in the
pass band, and the minimum required attenuation in the
stop band, respectively. The LOPASS part provides one
input and one output.
Figure 35 shows an example of a LOPASS filter device.
The filter provides a pass band cutoff of 800 Hz and a stop
Figure 35 LOPASS filter example.
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Chapter 6 Analog behavioral modeling
band cutoff of 1.2 kHz. The pass band ripple is 0.1 dB and
the minimum stop band attenuation is 50 dB. Assuming
that the input to the filter is the voltage at net 10 and
output is a voltage between nets 5 and 0, this will produce
a PSpice netlist declaration like this:
ELOWPASS 5 0 CHEBYSHEV {V(10)} = LP 800 1.2K .1dB 50dB
HIPASS
FS
stop band frequency
FP
pass band frequency
RIPPLE
pass band ripple in dB
STOP
stop band attenuation in dB
The HIPASS part is characterized by two cutoff
frequencies that delineate the boundaries of the filter pass
band and stop band. The attenuation values, RIPPLE and
STOP, define the maximum allowable attenuation in the
pass band, and the minimum required attenuation in the
stop band, respectively. The HIPASS part provides one
input and one output.
Figure 36 HIPASS filter part example.
Figure 36 shows an example of a HIPASS filter device.
This is a high pass filter with the pass band above 1.2 kHz
and the stop band below 800 Hz. Again, the pass band
ripple is 0.1 dB and the minimum stop band attenuation is
50 dB. This will produce a PSpice netlist declaration like
this:
EHIGHPASS 5 0 CHEBYSHEV {V(10)} = HP 1.2K 800 .1dB 50dB
BANDPASS
RIPPLE
pass band ripple in dB
STOP
stop band attenuation in dB
F0, F1,
F2, F3
cutoff frequencies
The BANDPASS part is characterized by four cutoff
frequencies. The attenuation values, RIPPLE and STOP,
define the maximum allowable attenuation in the pass
band, and the minimum required attenuation in the stop
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Control system parts
band, respectively. The BANDPASS part provides one
input and one output.
Figure 37 shows an example of a BANDPASS filter device.
This is a band pass filter with the pass band between 1.2
kHz and 2 kHz, and stop bands below 800 Hz and above
3 kHz. The pass band ripple is 0.1 dB and the minimum
stop band attenuation is 50 dB. This will produce a PSpice
netlist declaration like this:
Figure 37 BANDPASS filter part example.
EBANDPASS 5 0 CHEBYSHEV
+ {V(10)} = BP 800 1.2K 2K 3K .1dB 50dB
BANDREJ
RIPPLE
is the pass band ripple in dB
STOP
is the stop band attenuation in dB
F0, F1,
F2, F3
are the cutoff frequencies
The BANDREJ part is characterized by four cutoff
frequencies. The attenuation values, RIPPLE and STOP,
define the maximum allowable attenuation in the pass
band, and the minimum required attenuation in the stop
band, respectively. The BANDREJ part provides one
input and one output.
Figure 38 shows an example of a BANDREJ filter device.
This is a band reject (or “notch”) filter with the stop band
between 1.2 kHz and 2 kHz, and pass bands below 800 Hz
and above 3 kHz. The pass band ripple is 0.1 dB and the
minimum stop band attenuation is 50 dB. This will
produce a PSpice netlist declaration like this:
Figure 38 BANDREJ filter part example.
ENOTCH 5 0 CHEBYSHEV {V(10)} = BR 1.2K 800 3K 2K .1dB 50dB
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Chapter 6 Analog behavioral modeling
Integrator and differentiator
The integrator and differentiator parts are described
below.
INTEG
IC
initial condition of the integrator output
GAIN
gain value
The INTEG part implements a simple integrator. A
current source/capacitor implementation is used to
provide support for setting the initial condition.
DIFFER
GAIN
gain value
The DIFFER part implements a simple differentiator. A
voltage source/capacitor implementation is used. The
DIFFER part provides one input and one output.
Table look-up parts
TABLE and FTABLE parts provide a lookup table that is
used to correlate an input and an output based on a set of
data points. These parts are described below and on the
following pages.
TABLE
If more than five values are required, the
part can be customized through the part
editor. Insert additional row variables into
the template using the same form as the
first five, and add ROWn properties as
needed to the list of properties.
ROWn
is an (input, output) pair; by default, up to
five triplets are allowed where n=1, 2, 3, 4,
or 5
The TABLE part allows the response to be defined by a
table of one to five values. Each row contains an input and
a corresponding output value. Linear interpolation is
performed between entries.
For values outside the table’s range, the device’s output is
a constant with a value equal to the entry with the smallest
(or largest) input. This characteristic can be used to
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Control system parts
impose an upper and lower limit on the output. The
TABLE part provides one input and one output.
FTABLE
ROWn
either an (input frequency, magnitude,
phase) triplet, or an (input frequency, real
part, imaginary part) triplet describing a
complex value; by default, up to five
triplets are allowed where n=1, 2, 3, 4, or
5
DELAY
group delay increment; defaults to 0 if
left blank
R_I
table type; if left blank, the frequency
table is interpreted in the (input
frequency, magnitude, phase) format; if
defined with any value (such as YES), the
table is interpreted in the (input
frequency, real part, imaginary part)
format
MAGUNITS
units for magnitude where the value can
be DB (decibels) or MAG (raw
magnitude); defaults to DB if left blank
PHASEUNITS
units for phase where the value can be
DEG (degrees) or RAD (radians); defaults
to DEG if left blank
If more than five values are required, the
part can be customized through the part
editor. Insert additional row variables into
the template using the same form as the
first five, and add ROWn properties as
needed to the list of properties.
The FTABLE part is described by a table of frequency
responses in either the magnitude/phase domain (R_I= )
or complex number domain (R_I=YES). The entire table is
read in and converted to magnitude in dB and phase in
degrees.
Interpolation is performed between entries. Magnitude is
interpolated logarithmically; phase is interpolated
linearly. For frequencies outside the table’s range, 0 (zero)
magnitude is used. This characteristic can be used to
impose an upper and lower limit on the output.
The DELAY property increases the group delay of the
frequency table by the specified amount. The delay term
is particularly useful when a frequency table device
generates a non-causality warning message during a
transient analysis. The warning message issues a delay
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Chapter 6 Analog behavioral modeling
value that can be assigned to the part’s DELAY property
for subsequent runs, without otherwise altering the table.
The output of the part depends on the analysis being
done. For DC and bias point, the output is the zero
frequency magnitude times the input voltage. For AC
analysis, the input voltage is linearized around the bias
point (similar to EVALUE and GVALUE parts, Modeling
mathematical or instantaneous relationships on page 6-176).
The output for each frequency is then the input times the
gain, times the value of the table at that frequency.
For transient analysis, the voltage is evaluated at each
time point. The output is then the convolution of the past
values with the impulse response of the frequency
response. These rules follow the standard method of using
Fourier transforms. We recommend looking at one or
more of the references cited in Frequency-domain device
models on page 6-181 for more information.
Note
The table’s frequencies must be in order from lowest to highest. The
TABLE part provides one input and one output.
Example
Figure 39 FTABLE part example.
162
A device, ELOFILT, is used as a frequency filter. The input
to the frequency response is the voltage at net 10. The
output is a voltage across nets 5 and 0. The table describes
a low pass filter with a response of 1 (0 dB) for frequencies
below 5 kilohertz and a response of 0.001 (-60 dB) for
frequencies above 6 kilohertz. The phase lags linearly with
frequency. This is the same as a constant time delay. The
delay is necessary so that the impulse response is causal.
That is, so that the impulse response does not have any
significant components before time zero. The FTABLE
part in Figure 39 could be used.
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Control system parts
This part is characterized by the following properties:
ROW1 = 0Hz
ROW2 = 5kHz
ROW3 = 6kHz
DELAY =
R_I =
MAGUNITS =
PHASEUNITS =
0
0
-60
0
-5760
-6912
Since R_I, MAGUNITS, and PHASEUNITS are undefined,
each table entry is interpreted as containing frequency,
magnitude value in dB, and phase values in degrees.
Delay defaults to 0.
This produces a PSpice netlist declaration like this:
ELOFILT 5 0 FREQ {V(10)} = (0,0,0) (5kHz,0,-5760)
+ (6kHz,-60,-6912)
Since constant group delay is calculated from the values
for a given table entry as:
group delay = phase / 360 / frequency
An equivalent FTABLE instance could be defined using
the DELAY property. For this example, the group delay is
3.2 msec (6912 / 360 / 6k = 5760 / 360 / 6k = 3.2m).
Equivalent property assignments are:
ROW1 = 0Hz
ROW2 = 5kHz
ROW3 = 6kHz
DELAY = 3.2ms
R_I =
MAGUNITS =
PHASEUNITS =
0
0
-60
0
0
0
This produces a PSpice netlist declaration like this:
ELOFILT 5 0 FREQ {V(10)} = (0,0,0) (5kHz,0,0) (6kHz,-60,0)
+ DELAY=3.2ms
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Chapter 6 Analog behavioral modeling
Laplace transform part
The LAPLACE part specifies a Laplace transform which is
used to determine an output for each input value.
LAPLACE
NUM
numerator of the Laplace expression
DENOM
denominator of the Laplace expression
The LAPLACE part uses a Laplace transform description.
The input to the transform is a voltage. The numerator
and denominator of the Laplace transform function are
specified as properties for the part.
Note
Voltages, currents, and TIME may not appear in a Laplace
transform specification.
The output of the part depends on the type of analysis
being done. For DC and bias point, the output is the zero
frequency gain times the value of the input. The zero
frequency gain is the value of the Laplace transform with
s=0. For AC analysis, the output is then the input times the
gain times the value of the Laplace transform. The value
of the Laplace transform at a frequency is calculated by
substituting j·ω for s, where ω is 2π·frequency. For
transient analysis, the output is the convolution of the
input waveform with the impulse response of the
transform. These rules follow the standard method of
using Laplace transforms.
Example one
The input to the Laplace transform is the voltage at net 10.
The output is a voltage and is applied between nets 5 and
0. For DC, the output is simply equal to the input, since the
gain at s = 0 is 1. The transform, 1/(1+.001·s), describes a
simple, lossy integrator with a time constant of 1
millisecond. This can be implemented with an RC pair
that has a time constant of 1 millisecond.
For AC analysis, the gain is found by substituting j·ω for s.
This gives a flat response out to a corner frequency of
1000/(2π) = 159 hertz and a roll-off of 6 dB per octave after
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Control system parts
159 Hz. There is also a phase shift centered around 159 Hz.
In other words, the gain has both a real and an imaginary
component. For transient analysis, the output is the
convolution of the input waveform with the impulse
response of 1/(1+.001·s). The impulse response is a
decaying exponential with a time constant of 1
millisecond. This means that the output is the “lossy
integral” of the input, where the loss has a time constant
of 1 millisecond. The LAPLACE part shown in Figure 40
could be used for this purpose.
The transfer function is the Laplace transform
(1/[1+.001*s]). This LAPLACE part is characterized by the
following properties:
Figure 40 LAPLACE part example one.
NUM = 1
DENOM = 1 + .001*s
The gain and phase characteristics are shown in Figure 41.
Figure 41 Viewing gain and phase characteristics of a lossy
integrator.
This produces a PSpice netlist declaration like this:
ERC
5 0 LAPLACE {V(10)} = {1/(1+.001*s)}
Example two
The input is V(10). The output is a current applied
between nets 5 and 0. The Laplace transform describes a
Figure 42 LAPLACE part example two.
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Chapter 6 Analog behavioral modeling
lossy transmission line. R, L, and C are the resistance,
inductance, and capacitance of the line per unit length.
If R is small, the characteristic impedance of such a line is
Z = ((R + j·ω·L)/(j·ω·C))1/2, the delay per unit length is
(L C)1/2, and the loss in dB per unit length is 23·R/Z. This
could be represented by the device in Figure 42.
The parameters R, L, and C can be defined in a .PARAM
statement contained in a model file. (Refer to the online
OrCA D PSpice A /D Reference Manual for more information
about using .PARAM statements.) More useful, however,
is for R, L, and C to be arguments passed into a subcircuit.
This part has the following characteristics:
NUM = EXP(-SQRT(C*s*(R+L*s)))
DENOM = 1
This produces a PSpice netlist declaration like this:
GLOSSY 5 0 LAPLACE {V(10)} = {exp(-sqrt(C*s*(R + L*s)))}
The Laplace transform parts are, however, an inefficient
way, in both computer time and memory, to implement a
delay. For ideal delays we recommend using the
transmission line part instead.
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Control system parts
Math functions
The ABM math function parts are shown in Table 1. For
each device, the corresponding template is shown,
indicating the order in which the inputs are processed, if
applicable.
Table 1
ABM math function parts
For this device...
Output is the...
ABS
absolute value of the input
SQRT
square root of the input
PWR
result of raising the absolute value of the
input to the power specified by EXP
PWRS
result of raising the (signed) input value to
the power specified by EXP
LOG
LOG of the input
LOG10
LOG10 of the input
EXP
result of e raised to the power specified by
the input value (ex where x is the input)
SIN
sin of the input (where the input is in
radians)
COS
cos of the input (where the input is in
radians)
TAN
tan of the input (where the input is in
radians)
ATAN,
ARCTAN
tan-1 of the input (where the output is in
radians)
Math function parts are based on the PSpice “E” device
type. Each provides one or more inputs, and a
mathematical function which is applied to the input. The
result is output on the output net.
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Chapter 6 Analog behavioral modeling
ABM expression parts
The expression parts are shown in Table 2. These parts can
be customized to perform a variety of functions
depending on your requirements. Each of these parts has
a set of four expression building block properties of the
form:
EXPn
where n = 1, 2, 3, or 4.
During netlist generation, the complete expression is
formed by concatenating the building block expressions
in numeric order, thus defining the transfer function.
Hence, the first expression fragment should be assigned to
the EXP1 property, the second fragment to EXP2, and so
on.
Expression properties can be defined using a combination
of arithmetic operators and input designators. You may
use any of the standard PSpice arithmetic operators (see
Table 9 on page 3-70) within an expression statement. You
may also use the EXPn properties as variables to represent
nets or constants.
Table 2
ABM expression parts
Part
Inputs
Output
ABM
none
V
ABM1
1
V
ABM2
2
V
ABM3
3
V
ABM/I
none
I
ABM1/I
1
I
ABM2/I
2
I
ABM3/I
3
I
The following examples illustrate a variety of ABM
expression part applications.
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Control system parts
Example one
Suppose you want to set an output voltage on net 4 to 5
volts times the square root of the voltage between nets 3
and 2. You could use an ABM2 part (which takes two
inputs and provides a voltage output) to define a part like
the one shown in Figure 43.
In this example of an ABM device, the output voltage is set
to 5 volts times the square root of the voltage between
net 3 and net 2. The property settings for this part are as
follows:
Figure 43 ABM expression part
example one.
EXP1 = 5V *
EXP2 = SQRT(V(%IN2,%IN1))
This will produce a PSpice netlist declaration like this:
ESQROOT 4 0 VALUE = {5V*SQRT(V(3,2))}
Example two
GPSK is an oscillator for a PSK (Phase Shift Keyed)
modulator. Current is pumped from net 11 through the
source to net 6. Its value is a sine wave with an amplitude
of 15 mA and a frequency of 10 kHz. The voltage at net 3
can shift the phase of GPSK by 1 radian/volt. Note the use
of the TIME parameter in the EXP2 expression. This is the
PSpice internal sweep variable used in transient analyses.
For any analysis other than transient, TIME = 0. This could
be represented with an ABM1/I part (single input, current
output) like the one shown in Figure 44.
Figure 44 ABM expression part
example two.
This part is characterized by the following properties:
EXP1 = 15ma * SIN(
EXP2 = 6.28*10kHz*TIME
EXP3 = + V(%IN))
This produces a PSpice netlist declaration like this:
GPSK
11 6 VALUE = {15MA*SIN(6.28*10kHz*TIME+V(3))}
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Chapter 6 Analog behavioral modeling
Example three
Figure 45 ABM expression part
example three.
A device, EPWR, computes the instantaneous power by
multiplying the voltage across nets 5 and 4 by the current
through VSENSE. Sources are controlled by expressions
which may contain voltages or currents or both. The
ABM2 part (two inputs, current output) in Figure 45 could
represent this.
This part is characterized by the following properties:
EXP1 = V(%IN2,%IN1) *
EXP2 = I(VSENSE)
This produces a PSpice netlist declaration like this:
EPWR
3 0 VALUE = {V(5,4)*I(VSENSE)}
Example four
The output of a component, GRATIO, is a current whose
value (in amps) is equal to the ratio of the voltages at nets
13 and 2. If V(2) = 0, the output depends upon V(13) as
follows:
if V(13) = 0, output = 0
if V(13) > 0, output = MAXREAL
if V(13) < 0, output = -MAXREAL
Figure 46 ABM expression part
example four.
where MAXREAL is a PSpice internal constant
representing a very large number (on the order of 1e30). In
general, the result of evaluating an expression is limited to
MAXREAL. This is modeled with an ABM2/I (two input,
current output) part like this one in Figure 46.
This part is characterized by the following properties:
EXP1 = V(%IN2)/V(%IN1)
Note that output of GRATIO can be used as part of the
controlling function. This produces a PSpice netlist
declaration like this:
GRATIO 2 3 VALUE = {V(13)/V(2)}
Note
170
Letting a current approach ±1e30 will almost certainly cause
convergence problems. To avoid this, use the limit function on the
ratio to keep the current within reasonable limits.
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Control system parts
An instantaneous device example: modeling a
triode
This section provides an example of using various ABM
parts to model a triode vacuum tube. The schematic of the
triode subcircuit is shown in Figure 47.
Figure 47 Triode circuit.
Assumptions: In its main operating region, the triode’s
current is proportional to the 3/2 power of a linear
combination of the grid and anode voltages:
ianode = k0*(vg + k1*va)1.5
For a typical triode, k0 = 200e-6 and k1 = 0.12.
Looking at the upper left-hand portion of the schematic,
notice the a general-purpose ABM part used to take the
input voltages from anode, grid, and cathode. Assume the
following associations:
•
V(anode) is associated with V(%IN1)
•
V(grid) is associated with V(%IN2)
•
V(cathode) is associated with V(%IN3)
The expression property EXP1 then represents V(grid,
cathode) and the expression property EXP2 represents
0.12[V(anode, cathode)]. When the template substitution
is performed, the resulting VALUE is equivalent to the
following:
V = V(grid, cathode) + 0.12*V(anode, cathode)
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Chapter 6 Analog behavioral modeling
The part would be defined with the following
characteristics:
EXP1 = V(%IN2,%IN3)+
EXP2 = 0.12*V(%IN1,%IN3)
This works for the main operating region but does not
model the case in which the current stays 0 when
combined grid and anode voltages go negative. We can
accommodate that situation as follows by adding the
LIMIT part with the following characteristics:
HI = 1E3
LO = 0
This part instance, LIMIT1, converts all negative values of
vg+.12*va to 0 and leaves all positive values (up to 1 kV)
alone. For a more realistic model, we could have used
TABLE to correctly model how the tube turns off at 0 or at
small negative grid voltages.
We also need to make sure that the current becomes zero
when the anode alone goes negative. To do this, we can
use a DIFF device, (immediately below the ABM3 device)
to monitor the difference between V(anode) and
V(cathode), and output the difference to the TABLE part.
The table translates all values at or below zero to zero, and
all values greater than or equal to 30 to one. All values
between 0 and 30 are linearly interpolated. The properties
for the TABLE part are as follows:
ROW1 = 00
ROW2 = 301
The TABLE part is a simple one, and ensures that only a
zero value is output to the multiplier for negative anode
voltages.
The output from the TABLE part and the LIMIT part are
combined at the MULT multiplier part. The output of the
MULT part is the product of the two input voltages. This
value is then raised to the 3/2 or 1.5 power using the PWR
part. The exponential property of the PWR part is defined
as follows:
EXP = 1.5
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Control system parts
The last major component is an ABM expression
component to take an input voltage and convert it into a
current. The relevant ABM1/I part property looks like
this:
EXP1 = 200E-6 * V(%IN)
A final step in the model is to add device parasitics. For
example, a resistor can be used to give a finite output
impedance. Capacitances between the grid, cathode, and
anode are also needed. The lower part of the schematic in
Figure 47 shows a possible method for incorporating
these effects. To complete the example, one could add a
circuit which produces the family of I-V curves (shown in
Figure 48).
Figure 48 Triode subcircuit producing a family of I-V curves.
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Chapter 6 Analog behavioral modeling
PSpice-equivalent parts
PSpice-equivalent parts respond to a differential input
and have double-ended output. These parts reflect the
structure of PSpiceE and G devices, thus having two pins
for each controlling input and the output in the part.
Table 1 summarizes the PSpice-equivalent parts available
in the part library.
Table 1
PSpice-equivalent parts
Category
Part
Description
Properties
Mathematical
expression
EVALUE
general purpose
EXPR
special purpose
(none)
general purpose
EXPR
GVALUE
ESUM
GSUM
EMULT
GMULT
Table look-up
ETABLE
GTABLE
There are no equivalent “F” or “H” part
types in the part library becayse PSpice “F”
and “H” devices do not support the ABM
extensions.
174
Frequency
table look-up
EFREQ
Laplace
transform
ELAPLACE
TABLE
general purpose
GFREQ
GLAPLACE
EXPR
TABLE
general purpose
EXPR
XFORM
PSpice-equivalent ABM parts can be classified as either E
or G device types. The E part type provides a voltage
output, and the G device type provides a current output.
The device’s transfer function can contain any mixture of
voltages and currents as inputs. Hence, there is no longer
a division between voltage-controlled and
current-controlled parts. Rather the part type is dictated
only by the output requirements. If a voltage output is
required, use an E part type. If a current output is
necessary, use a G part type.
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PSpice-equivalent parts
Each E or G part type in the ABM.OLB part file is defined
by a template that provides the specifics of the transfer
function. Other properties in the model definition can be
edited to customize the transfer function. By default, the
template cannot be modified directly choosing Properties
from the Edit menu in Capture. Rather, the values for
other properties (such as the expressions used in the
template) are usually edited, then these values are
substituted into the template. However, the part editor
can be used to modify the template or designate the
template as modifiable from within Capture. This way,
custom parts can be created for special-purpose
application.
Implementation of PSpice-equivalent parts
Although you generally use Capture to place and specify
PSpice-equivalent ABM parts, it is useful to know the
PSpice command syntax for “E” and “G” devices. This is
especially true when creating custom ABM parts since
part templates must adhere to PSpice syntax.
The general forms for PSpice “E” and “G” extensions are:
E <name> <connecting nodes> <ABM keyword> <ABM function>
G <name> <connecting nodes> <ABM keyword> <ABM function>
where
<name>
is the device name appended to the E
or G device type character
<connecting
nodes>
specifies the <(+ node name, - node
name)> pair between which the
device is connected
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Chapter 6 Analog behavioral modeling
<A BM
keyword>
specifies the form of the transfer
function to be used, as one of:
VALUE
TABLE
LAPLACE
FREQ
table
CHEBYSHEV
<A BM
function>
arithmetic expression
lookup table
Laplace transform
frequency response
Chebyshev filter
characteristics
specifies the transfer function as a
formula or lookup table as required
by the specified <ABM keyword>
Refer to the online OrCA D PSpice A /D Reference Manual for
detailed information.
Modeling mathematical or instantaneous
relationships
The instantaneous models (using VALUE and TABLE
extensions to PSpice “E” and “G” devices in the part
templates) enforce a direct response to the input at each
moment in time. For example, the output might be equal
to the square root of the input at every point in time. Such
a device has no memory, or, a flat frequency response.
These techniques can be used to model both linear and
nonlinear responses.
Note
For AC analysis, a nonlinear device is first linearized around the
bias point, and then the linear equivalent is used.
EVALUE and GVALUE parts
The EVALUE and GVALUE parts allow an instantaneous
transfer function to be written as a mathematical
expression in standard notation. These parts take the
input signal, perform the function specified by the EXPR
property on the signal, and output the result on the output
pins.
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PSpice-equivalent parts
In controlled sources, EXPR may contain constants and
parameters as well as voltages, currents, or time. Voltages
may be either the voltage at a net, such as V(5), or the
voltage across two nets, such as V(4,5). Currents must be
the current through a voltage source (V device), for
example, I(VSENSE). Voltage sources with a value of 0 are
handy for sensing current for use in these expressions.
Functions may be used in expressions, along with
arithmetic operators (+, -, *, and /) and parentheses.
Available built-in functions are summarized in Table 10
on page 3-71.
The EVALUE and GVALUE parts are defined, in part, by
the following properties (default values are shown):
EVALUE
EXPR
V(%IN+, %IN-)
GVALUE
EXPR
V(%IN+, %IN-)
Sources are controlled by expressions which may contain
voltages, currents, or both. The following examples
illustrate customized EVALUE and GVALUE parts.
Example 1
In the example of an EVALUE device shown in Figure 49,
the output voltage is set to 5 volts times the square root of
the voltage between pins %IN+ and %IN-.
The property settings for this device are as follows:
EXPR = 5v * SQRT(V(%IN+,%IN-))
Figure 49 EVALUE part example.
Example 2
Consider the device in Figure 50. This device could be
used as an oscillator for a PSK (Phase Shift Keyed)
modulator.
A current through a source is a sine wave with an
amplitude of 15 mA and a frequency of 10 kHz. The
voltage at the input pin can shift the phase by 1
radian/volt. Note the use of the TIME parameter in this
Figure 50 GVALUE part example.
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Chapter 6 Analog behavioral modeling
expression. This is the PSpice internal sweep variable
used in transient analyses. For any analysis other than
transient, TIME = 0. The relevant property settings for this
device are shown below:
EXPR = 15ma*SIN(6.28*10kHz*TIME+V(%IN+,%IN-))
EMULT, GMULT, ESUM, and GSUM
The EMULT and GMULT parts provide output which is
based on the product of two input sources. The ESUM and
GSUM parts provide output which is based on the sum of
two input sources. The complete transfer function may
also include other mathematical expressions.
Example 1
Figure 51 EMULT part example.
Consider the device in Figure 51. This device computes
the instantaneous power by multiplying the voltage
across pins %IN+ and %IN- by the current through
VSENSE. This device’s behavior is built-in to the
PSPICETEMPLATE property as follows (appears on one
line):
TEMPLATE=E^@REFDES %OUT+ %OUT- VALUE {V(%IN1+,%IN1-)
*V(%IN2+,%IN2-)}
You can use the part editor to change the characteristics of
the template to accommodate additional mathematical
functions, or to change the nature of the transfer function
itself. For example, you may want to create a voltage
divider, rather than a multiplier. This is illustrated in the
following example.
Example 2
Consider the device in Figure 52.
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PSpice-equivalent parts
Figure 52 GMULT part example.
With this device, the output is a current is equal to the
ratio of the voltages at input pins 1 and input pins 2. If
V(%IN2+, %IN2-) = 0, the output depends upon V(%IN1+,
%IN1-) as follows:
if V(%IN1+, %IN1-) = 0, output = 0
if V(%IN1+, %IN1-) > 0, output = MAXREAL
if V(%IN1+, %IN1-) < 0, output = -MAXREAL
where MAXREAL is a PSpice internal constant
representing a very large number (on the order of 1e30). In
general, the result of evaluating an expression is limited to
MAXREAL. Note that the output of the part can also be
used as part of the controlling function.
To create this device, you would first make a new part,
GDIV, based on the GMULT part. Edit the GDIV template
to divide the two input values rather than multiply them.
Lookup tables (ETABLE and GTABLE)
The ETABLE and GTABLE parts use a transfer function
described by a table. These device models are well suited
for use with measured data.
The ETABLE and GTABLE parts are defined in part by the
following properties (default values are shown):
ETABLE
TABLE
EXPR
(-15, -15), (15,15)
V(%IN+, %IN-)
GTABLE
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Chapter 6 Analog behavioral modeling
TABLE
EXPR
(-15, -15), (15,15)
V(%IN+, %IN-)
First, EXPR is evaluated, and that value is used to look up
an entry in the table. EXPR is a function of the input
(current or voltage) and follows the same rules as for
VALUE expressions.
The table consists of pairs of values, the first of which is an
input, and the second of which is the corresponding
output. Linear interpolation is performed between entries.
For values of EXPR outside the table’s range, the device’s
output is a constant with a value equal to the entry with
the smallest (or largest) input. This characteristic can be
used to impose an upper and lower limit on the output.
An example of a table declaration (using the TABLE
property) would be the following:
TABLE =
+ (0, 0) (.02, 2.690E-03) (.04, 4.102E-03) (.06, 4.621E-03)
+ (.08, 4.460E-03) (.10, 3.860E-03) (.12, 3.079E-03) (.14,
+ 2.327E-03)
+ (.16, 1.726E-03) (.18, 1.308E-03) (.20, 1.042E-03) (.22,
+ 8.734E-04)
+ (.24, 7.544E-04) (.26, 6.566E-04) (.28, 5.718E-04) (.30,
+ 5.013E-04)
+ (.32, 4.464E-04) (.34, 4.053E-04) (.36, 3.781E-04) (.38,
+ 3.744E-04)
+ (.40, 4.127E-04) (.42, 5.053E-04) (.44, 6.380E-04) (.46,
+ 7.935E-04)
+ (.48, 1.139E-03) (.50, 2.605E-03) (.52, 8.259E-03) (.54,
+ 2.609E-02)
+ (.56, 7.418E-02) (.58, 1.895E-01) (.60, 4.426E-01)
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PSpice-equivalent parts
Frequency-domain device models
Frequency-domain models (ELAPLACE, GLAPLACE,
EFREQ, and GFREQ) are characterized by output that
depends on the current input as well as the input history.
The relationship is therefore non-instantaneous. For
example, the output may be equal to the integral of the
input over time. In other words, the response depends
upon frequency.
During AC analysis, the frequency response determines
the complex gain at each frequency. During DC analysis
and bias point calculation, the gain is the zero-frequency
response. During transient analysis, the output of the
device is the convolution of the input and the impulse
response of the device.
Laplace transforms (LAPLACE)
The ELAPLACE and GLAPLACE parts allow a transfer
function to be described by a Laplace transform function.
The ELAPLACE and GLAPLACE parts are defined, in
part, by the following properties (default values are
shown):
ELAPLACE
EXPR
XFORM
Moving back and forth between the time
and frequency-domains can cause
surprising results. Often the results are
quite different than what one would
intuitively expect. For this reason, we
strongly recommend familiarity with a
reference on Fourier and Laplace
transforms. A good one is:
1 R. Bracewell, The Fourier Transform
and Its Applications, McGraw-Hill,
Revised Second Edition (1986)
We also recommend familiarity with the
use of transforms in analyzing linear
systems. Some references on this subject:
2 W. H. Chen, The Analysis of Linear
Systems, McGraw-Hill (1962)
3 J. A. Aseltine, Transform Method in
Linear System Analysis, McGraw-Hill
(1958)
4 G. R. Cooper and C. D. McGillen,
Methods of Signal and System
Analysis, Holt, Rinehart, and Winston
(1967)
V(%IN+, %IN-)
1/s
GLAPLACE
EXPR
XFORM
V(%IN+, %IN-)
1/s
The LAPLACE parts use a Laplace transform description.
The input to the transform is the value of EXPR, where
EXPR follows the same rules as for VALUE expressions
(see EVALUE and GVALUE parts on page 6-176). XFORM is
an expression in the Laplace variable, s. It follows the rules
for standard expressions as described for VALUE
expressions with the addition of the s variable.
Voltages, currents, and TIME cannot appear
in a Laplace transform.
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Chapter 6 Analog behavioral modeling
The output of the device depends on the type of analysis
being done. For DC and bias point, the output is simply
the zero frequency gain times the value of EXPR. The zero
frequency gain is the value of XFORM with s = 0. For AC
analysis, EXPR is linearized around the bias point (similar
to the VALUE parts). The output is then the input times
the gain of EXPR times the value of XFORM. The value of
XFORM at a frequency is calculated by substituting j·w for
s, where w is 2p·frequency. For transient analysis, the
value of EXPR is evaluated at each time point. The output
is then the convolution of the past values of EXPR with the
impulse response of XFORM. These rules follow the
standard method of using Laplace transforms. We
recommend looking at one or more of the references cited
in Frequency-domain device models on page 6-181 for more
information.
Example
The input to the Laplace transform is the voltage across
the input pins, or V(%IN+, %IN-). The EXPR property
may be edited to include constants or functions, as with
other parts. The transform, 1/(1+.001·s), describes a
simple, lossy integrator with a time constant of 1
millisecond. This can be implemented with an RC pair
that has a time constant of 1 millisecond.
Using the part editor, you would define the XFORM and
EXPR properties as follows:
XFORM = 1/(1+.001*s)
EXPR = V(%IN+, %IN-)
The default template remains (appears on one line):
TEMPLATE= E^@REFDES %OUT+ %OUT- LAPLACE
{@EXPR}= (@XFORM)
After netlist substitution of the template, the resulting
transfer function would become:
V(%OUT+, %OUT-) = LAPLACE {V(%IN+, %IN-)}= (1/1+.001*s))
The output is a voltage and is applied between pins
%OUT+ and %OUT-. For DC, the output is simply equal
to the input, since the gain at s = 0 is 1.
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PSpice-equivalent parts
For AC analysis, the gain is found by substituting j·ω for s.
This gives a flat response out to a corner frequency of
1000/(2π) = 159 Hz and a roll-off of 6 dB per octave after
159 Hz. There is also a phase shift centered around 159 Hz.
In other words, the gain has both a real and an imaginary
component. The gain and phase characteristic is the same
as that shown for the equivalent control system part
example using the LAPLACE part (see Figure 41 on
page 6-165).
For transient analysis, the output is the convolution of the
input waveform with the impulse response of
1/(1+.001·s). The impulse response is a decaying
exponential with a time constant of 1 millisecond. This
means that the output is the “lossy integral” of the input,
where the loss has a time constant of 1 millisecond.
This will produce a PSpice netlist declaration similar to:
ERC 5 0 LAPLACE {V(10)} = {1/(1+.001*s)}
Frequency response tables (EFREQ and GFREQ)
The EFREQ and GFREQ parts are described by a table of
frequency responses in either the magnitude/phase
domain or complex number domain. The entire table is
read in and converted to magnitude in dB and phase in
degrees. Interpolation is performed between entries.
Phase is interpolated linearly; magnitude is interpolated
logarithmically. For frequencies outside the table’s range,
0 (zero) magnitude is used.
EFREQ and GFREQ properties are defined as follows:
EXPR
value used for table lookup; defaults
to V(%IN+, %IN-) if left blank.
TABLE
series of either (input frequency,
magnitude, phase) triplets, or (input
frequency, real part, imaginary part)
triplets describing a complex value;
defaults to (0,0,0) (1Meg,-10,90) if left
blank.
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Chapter 6 Analog behavioral modeling
DELAY
group delay increment; defaults to 0
if left blank.
R_I
table type; if left blank, the frequency
table is interpreted in the (input
frequency, magnitude, phase)
format; if defined with any value
(such as YES), the table is interpreted
in the (input frequency, real part,
imaginary part) format.
MAGUNITS
units for magnitude where the value
can be DB (decibels) or MAG (raw
magnitude); defaults to DB if left
blank.
PHASEUNITS
units for phase where the value can
be DEG (degrees) or RAD (radians);
defaults to DEG if left blank.
The DELAY property increases the group delay of the
frequency table by the specified amount. The delay term
is particularly useful when an EFREQ or GFREQ device
generates a non-causality warning message during a
transient analysis. The warning message issues a delay
value that can be assigned to the part’s DELAY property
for subsequent runs, without otherwise altering the table.
The output of the device depends on the analysis being
done. For DC and bias point, the output is simply the zero
frequency magnitude times the value of EXPR. For AC
analysis, EXPR is linearized around the bias point (similar
to EVALUE and GVALUE parts). The output for each
frequency is then the input times the gain of EXPR times
the value of the table at that frequency. For transient
analysis, the value of EXPR is evaluated at each time
point. The output is then the convolution of the past
values of EXPR with the impulse response of the
frequency response. These rules follow the standard
method of using Fourier transforms. We recommend
looking at one or more of the references cited in
Frequency-domain device models on page 6-181 for more
information.
Note
184
The table’s frequencies must be in order from lowest to highest.
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PSpice-equivalent parts
Figure 53 shows an EFREQ device used as a low pass
filter. The input to the frequency response is the voltage
across the input pins. The table describes a low pass filter
with a response of 1 (0 dB) for frequencies below 5
kilohertz and a response of .001 (-60 dB) for frequencies
above 6 kilohertz. The output is a voltage across the
output pins.
Figure 53 EFREQ part example.
This part is defined by the following properties:
TABLE = (0, 0, 0) (5kHz, 0, -5760) (6kHz, -60, -6912)
DELAY =
R_I =
MAGUNITS =
PHASEUNITS =
Since R_I, MAGUNITS, and PHASEUNITS are undefined,
each table entry is interpreted as containing frequency,
magnitude value in dB, and phase values in degrees.
Delay defaults to 0.
The phase lags linearly with frequency meaning that this
table exhibits a constant time (group) delay. The delay is
necessary so that the impulse response is causal. That is,
so that the impulse response does not have any significant
components before time zero.
The constant group delay is calculated from the values for
a given table entry as follows:
group delay = phase / 360 / frequency
For this example, the group delay is 3.2 msec
(6912 / 360 / 6k = 5760 / 360 / 6k = 3.2m). An alternative
specification for this table could be:
TABLE = (0, 0, 0) (5kHz, 0, 0) (6kHz, -60, 0)
DELAY = 3.2ms
R_I =
MAGUNITS =
PHASEUNITS =
This produces a PSpice netlist declaration like this:
ELOWPASS 5 0 FREQ {V(10)} = (0,0,0) (5kHz,0,0) (6kHz-60,0)
+ DELAY = 3.2ms
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Chapter 6 Analog behavioral modeling
Cautions and recommendations
for simulation and analysis
Instantaneous device modeling
During AC analysis, nonlinear transfer functions are
handled the same way as other nonlinear parts: each
function is linearized around the bias point and the
resulting small-signal equivalent is used.
Consider the voltage multiplier (mixer) shown in
Figure 54. This circuit has the following characteristics:
Vin1:
Vin2:
DC=0v AC=1v
DC=0v AC=1v
where the output on net 3 is V(1)*V(2).
Figure 54 Voltage multiplier circuit
(mixer).
During AC analysis, V(3) = 0 due to the 0 volts bias point
voltage on nets 1, 2, and 3. The small-signal equivalent
therefore has 0 gain (the derivative of V(1)*V(2) with
respect to both V(1) and V(2) is 0 when V(1)=V(2)=0). So,
the output of the mixer during AC analysis will be 0
regardless of the AC values of V(1) and V(2).
Another way of looking at this is that a mixer is a
nonlinear device and AC analysis is a linear analysis. The
output of the mixer has 0 amplitude at the fundamental.
(Output is nonzero at DC and twice the input frequency,
but these are not included in a linear analysis.)
If you need to analyze nonlinear functions, such as a
mixer, use transient analysis. Transient analysis solves the
full, nonlinear circuit equations. It also allows you to use
input waveforms with different frequencies (for example,
VIN1 could be 90 MHz and VIN2 could be 89.8 MHz). AC
analysis does not have this flexibility, but in return it uses
much less computer time.
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Cautions and recommendations for simulation and analysis
Frequency-domain parts
Some caution is in order when moving between frequency
and time domains. This section discusses several points
that are involved in the implementation of
frequency-domain parts. These discussions all involve the
transient analysis, since both the DC and AC analyses are
straightforward.
The first point is that there are limits on the maximum
values and on the resolution of both time and frequency.
These are related: the frequency resolution is the inverse
of the maximum time and vice versa. The maximum time
is the length of the transient analysis, TSTOP. Therefore,
the frequency resolution is 1/TSTOP.
Laplace transforms
For Laplace transforms, PSpice starts off with initial
bounds on the frequency resolution and the maximum
frequency determined by the transient analysis
parameters as follows. The frequency resolution is
initially set below the theoretical limit to (.25/TSTOP) and
is then made as large as possible without inducing
sampling errors. The maximum frequency has an initial
upper bound of (1/(RELTOL*TMAX)), where TMAX is
the transient analysis Step Ceiling value, and RELTOL is
the relative accuracy of all calculated voltages and
currents. If a Step Ceiling value is not specified, PSpice
uses the Transient Analysis Print Step, TSTEP, instead.
PSpice then attempts to reduce the maximum frequency
by searching for the frequency at which the response has
fallen to RELTOL times the maximum response. For
instance, for the transform:
Note TSTOP, TMAX, and TSTEP values are
configured using Transient on the Setup
menu. The RELTOL property is set using
Options on the Setup menu.
1/(1+s)
the maximum response, 1.0, is at s = j·ω = 0 (DC). The
cutoff frequency used when RELTOL=.001, is
approximately 1000/(2π) = 159 Hz. At 159 Hz, the
response is down to .001 (down by 60 db). Since some
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Chapter 6 Analog behavioral modeling
transforms do not have such a limit, there is also a limit of
10/RELTOL times the frequency resolution, or
10/(RELTOL·TSTOP). For example, consider the
transform:
e-0.001·s
This is an ideal delay of 1 millisecond and has no
frequency cutoff. If TSTOP = 10 milliseconds and
RELTOL=.001, then PSpice imposes a frequency cutoff of
10 MHz. Since the time resolution is the inverse of the
maximum frequency, this is equivalent to saying that the
delay cannot resolve changes in the input at a rate faster
than .1 microseconds. In general, the time resolution will
be limited to RELTOL·TSTOP/10.
A final computational consideration for Laplace parts is
that the impulse response is determined by means of an
FFT on the Laplace expression. The FFT is limited to 8192
points to keep it tractable, and this places an additional
limit on the maximum frequency, which may not be
greater than 8192 times the frequency resolution.
If your circuit contains many Laplace parts which can be
combined into a more complex single device, it is
generally preferable to do this. This saves computation
and memory since there are fewer impulse responses. It
also reduces the number of opportunities for numerical
artifacts that might reduce the accuracy of your transient
analyses.
Laplace transforms can contain poles in the left half-plane.
Such poles will cause an impulse response that increases
with time instead of decaying. Since the transient analysis
is always for a finite time span, PSpice does not have a
problem calculating the transient (or DC) response.
However, such poles will make the actual device oscillate.
Non-causality and Laplace transforms
PSpice applies an inverse FFT to the Laplace expression to
obtain an impulse response, and then convolves the
impulse response with the dependent source input to
obtain the output. Some common impulse responses are
inherently non-causal. This means that the convolution
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Cautions and recommendations for simulation and analysis
must be applied to both past and future samples of the
input in order to properly represent the inverse of the
Laplace expression.
For example, the expression {S} corresponds to
differentiation in the time domain. The impulse response
for {S} is an impulse pair separated by an infinitesimal
distance in time. The impulses have opposite signs, and
are situated one in the infinitesimal past, the other in the
infinitesimal future. In other words, convolution with this
corresponds to applying a finite-divided difference in the
time domain.
The problem with this for PSpice is that the simulator only
has the present and past values of the simulated input, so
it can only apply half of the impulse pair during
convolution. This will obviously not result in
time-domain differentiation. PSpice can detect, but not fix
this condition, and issues a non-causality warning
message when it occurs. The message tells what
percentage of the impulse response is non-causal, and
how much delay would need to be added to slide the
non-causal part into a causal region. {S} is theoretically
50% non-causal. Non-causality on the order of 1% or less
is usually not critical to the simulation results.
You can delay {S} to keep it causal, but the separation
between the impulses is infinitesimal. This means that a
very small time step is needed. For this reason, it is usually
better to use a macromodel to implement differentiation.
Here are some guidelines:
•
In the case of a Laplace device (ELAPLACE), multiply
the Laplace expression by e to the
(-s ∗ <the suggested delay>).
•
In the case of a frequency table (EFREQ or GFREQ), do
either of the following:
•
Specify the table with
DELAY=<the suggested delay>.
•
Compute the delay by adding a phase shift.
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Chapter 6 Analog behavioral modeling
Chebyshev filters
All of the considerations given above for Laplace parts
also apply to Chebyshev filter parts. However, PSpice also
attempts to deal directly with inaccuracies due to
sampling by applying Nyquist criteria based on the
highest filter cutoff frequency. This is done by checking
the value of TMAX. If TMAX is not specified it is assigned
a value, or if it is specified, it may be reduced.
For low pass and band pass filters, TMAX is set to
(0.5/FS), where FS is the stop band cutoff in the case of a
low pass filter, or the upper stop band cutoff in the case of
a band pass filter.
For high pass and band reject filters, there is no clear way
to apply the Nyquist criterion directly, so an additional
factor of two is thrown in as a safety margin. Thus, TMAX
is set to (0.25/FP), where FP is the pass band cutoff for the
high pass case or the upper pass band cutoff for the band
reject case. It may be necessary to set TMAX to something
smaller if the filter input has significant frequency content
above these limits.
Frequency tables
For frequency response tables, the maximum frequency is
twice the highest value. It will be reduced to
10/(RELTOL⋅TSTOP) or 8192 times the frequency
resolution if either value is smaller.
The frequency resolution for frequency response tables is
taken to be either the smallest frequency increment in the
table or the fastest rate of phase change, whichever is least.
PSpice then checks to see if it can be loosened without
inducing sampling errors.
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Cautions and recommendations for simulation and analysis
Trading off computer resources for accuracy
There is a significant trade-off between accuracy and
computation time for parts modeled in the frequency
domain. The amount of computer time and memory scale
approximately inversely to RELTOL. Therefore, if you can
use RELTOL=.01 instead of the default .001, you will be
ahead. However, this will not adversely affect the impulse
response. You may also wish to vary TMAX and TSTOP,
since these also come into play.
Since the trade-off issues are fairly complex, it is advisable
to first simulate a small test circuit containing only the
frequency-domain device, and then after proper
validation, proceed to incorporate it in your larger design.
The PSpice defaults will be appropriate most of the time if
accuracy is your main concern, but it is still worth
checking.
Note
Do not set RELTOL to a value above 0.01. This can seriously
compromise the accuracy of your simulation.
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Chapter 6 Analog behavioral modeling
Basic controlled sources
As with basic SPICE, PSpice has basic controlled sources
derived from the standard SPICE E, F, G, and H devices.
Table 1 summarizes the linear controlled source types
provided in the standard part library.
Table 1
Basic controlled sources in ANALOG.OLB
Device type
Part name
Controlled Voltage Source
(PSpice E device)
E
Current-Controlled Current Source
(PSpice F device)
F
Controlled Current Source
(PSpice G device)
G
Current-Controlled Voltage Source
(PSpice H device)
H
Creating custom ABM parts
Refer to your OrCA D Capture
User’s Guide for a description of how
to create a custom part.
Create a custom part when you need a controlled source
that is not provided in the special purpose set or that is
more elaborate than you can build with the general
purpose parts (with multiple controlling inputs, for
example).
The transfer function can be built into the part two
different ways:
Refer to the online OrCA D PSpice
A /D Reference Manual for more
information about E and G devices.
192
•
directly in the PSPICETEMPLATE definition.
•
by defining the part’s EXPR and related properties (if
any).
The PSpice syntax for declaring E and G devices can help
you form a PSPICETEMPLATE definition.
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Part three
Setting Up and Running
Analyses
Part Three describes how to set up and run analyses and
provides setup information specific to each analysis type.
•
Chapter 7, Setting up analyses and starting simulation,
explains the procedures general to all analysis types to
set up and start the simulation.
•
Chapter 8, DC analyses, describes how to set up DC
analyses, including DC sweep, bias point detail, smallsignal DC transfer, and DC sensitivity.
•
Chapter 9, AC analyses, describes how to set up AC
sweep and noise analyses.
•
Chapter 10, Transient analysis, describes how to set up
transient analysis and optionally Fourier components.
This chapter also explains how to use the Stimulus
Editor to create time-based input.
•
Chapter 11, Parametric and temperature analysis,
describes how to set up parametric and temperature
analyses, and how to run post-simulation
performance analysis in Probe on the results of these
analyses.
Pspug.book Page 194 Wednesday, November 11, 1998 1:14 PM
•
Chapter 12, Monte Carlo and sensitivity/worst-case
analyses, describes how to set up Monte Carlo and
sensitivity/worst-case analyses for statistical
interpretation of your circuit’s behavior.
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Setting up analyses and
starting simulation
7
Chapter overview
This chapter provides an overview of setting up analyses
and starting simulation that applies to any analysis type.
The other chapters in Part three, Setting Up and Running
A nalyses provide specific analysis setup information for
each analysis type.
This chapter includes the following sections:
•
Analysis types on page 7-196
•
Setting up analyses on page 7-197
•
Starting a simulation on page 7-206
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Chapter 7 Setting up analyses and starting simulation
Analysis types
PSpice supports analyses that can simulate analog-only
circuits.
Table 2 provides a summary of the available PSpice
analyses and the corresponding Analysis type options
where the analysis parameters are specified. In Capture,
switch to the PSpice view, then from the PSpice menu,
choose New Simulation Profile .
Table 2
Classes of PSpice analyses
Analysis
Analysis type or Option Swept variable
Standard analyses
DC sweep
DC Sweep
source
parameter
temperature
Bias point
Bias Point
Small-signal DC transfer
Bias Point
DC sensitivity
Bias Point
Frequency response
AC Sweep/Noise
frequency
Noise (requires a frequency
response analysis)
AC Sweep/Noise
frequency
Transient response
Time Domain
(Transient)
time
Fourier (requires transient
response analysis)
Time Domain
(Transient)
time
Simple multi-run analyses
Parametric
Parametric Sweep
Temperature
Temperature
(Sweep)
Statistical analyses
196
Monte Carlo
Monte Carlo/
Worst Case
Sensitivity/worst-case
Monte Carlo/
Worst Case
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Setting up analyses
The waveform analyzer calculates and displays the results
of PSpice simulations for swept analyses. The waveform
analyzer also generates supplementary analysis
information in the form of lists and tables, and saves this
in the simulation output file.
See Part four, V iewing results, for
information about using waveform analysis
in PSpice.
Setting up analyses
To set up one or more analyses
1
From the PSpice menu, choose New Simulation
Profile.
2
Enter the name of the profile and click OK.
3
Click the Analysis tab if it is not already the active tab
in the dialog box.
4
Enter the necessary parameter values and select the
appropriate check boxes to complete the analysis
specifications.
Specific information for setting up each
type of analysis is discussed in the following
chapters.
See Output variables on
page 7-199 for a description of the
output variables that can be entered in the
Simulation Settings dialog box displayed
for an analysis type.
Specific information for setting up each
type of analysis is discussed in the following
chapters.
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Chapter 7 Setting up analyses and starting simulation
5
Set up any other analyses you want to perform for the
circuit by selecting any of the remaining analysis types
and options, then complete their setup dialog boxes.
Execution order for standard analyses
For normal simulations that are run from a simulation
profile, or in batch mode, only the particular analysis type
that is specified will be executed.
During simulation of a circuit file, the analysis types are
performed in the order shown in Table 3. Each type of
analysis is conducted only once per run.
Several of the analyses (small-signal transfer, DC
sensitivity, and frequency response) depend upon the bias
point calculation. Because so many analyses use the bias
point, PSpice calculates this automatically. PSpice’s bias
point calculation computes initial states of analog
components.
.Table 3
Execution order for standard analyses
1. DC sweep
2. Bias point
3. Frequency response
4. Noise
5. DC sensitivity
6. Small-signal DC transfer
7. Transient response
8. Fourier components
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Setting up analyses
Output variables
Certain analyses (such as noise, Monte Carlo, sensitivity/
worst-case, DC sensitivity, Fourier, and small-signal DC
transfer function) require you to specify output variables
for voltages and currents at specific points on the
schematic. Depending upon the analysis type, you may
need to specify the following:
•
Voltage on a net, a pin, or at a terminal of a
semiconductor device
•
Current through a part or into a terminal of a
semiconductor device
•
Adevice name
If output variables or other information are required,
select Output File Options in the Monte Carlo/Worst Case
dialog box and enter the required parameters.
Voltage
Specify voltage in the following format:
v[modifiers](<out id>[,<out id>])
(1)
where <out id > is:
<net id> or <pin id>
(2)
<net id> is a fully qualified net name
(3)
<pin id> is <fully qualified device name>:<pin name> (4)
A fully qualified net name (as referred to in line 3 above)
is formed by prefixing the visible net name (from a label
applied to one of the segments of a wire or bus, or an
offpage port connected to the net) with the full
hierarchical path, separated by periods. At the top level of
hierarchy, this is just the visible name.
A fully qualified device name (from line 4 above) is
distinguished by specifying the full hierarchical path
followed by the device’s part reference, separated by
period characters. For example, a resistor with part
reference R34 inside part Y1 placed on a top-level
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Chapter 7 Setting up analyses and starting simulation
schematic page is referred to as Y1.R34 when used in an
output variable.
A <pin id> (from line 4) is uniquely distinguished by
specifying the full part name (as described above)
followed by a colon, and the pin name. For example, the
pins on a capacitor with reference designator C31 placed
on a top-level page and pin names 1 and 2 would be
identified as C31:1 and C31:2, respectively.
Current
Specify current in the following format:
i[modifiers](<out device>[:modifiers])
where <out device> is a fully qualified device name.
Modifiers
The basic syntax for output variables can be modified to
indicate terminals of semiconductors and AC
specifications. The modifiers come before <out id> or
<out device>. Or, when specifying terminals (such as
source or drain), the modifier is the pin name contained in
<out id>, or is appended to <out device> separated by a
colon.
Modifiers can be specified as follows:
•
For voltage:
v[AC suffix](<out id>[, out id])
v[terminal]*(<out device>)
•
For current:
i[AC suffix](<out device>[:terminal])
i[terminal][AC suffix](<out device>])
where
terminal
200
specifies one or two terminals for devices
with more than two terminals, such as D
(drain), G (gate), S (source)
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Setting up analyses
AC suffix
specifies the quantity to be reported for an
AC analysis, such as M (magnitude), P
(phase), G (group delay)
out id
specifies either the <net id> or <pin id>
(<fully qualified device name>:<pin name>)
out device
specifies the <fully qualified device name>
These building blocks can be used for specifying output
variables as shown in Table 4 (which summarizes the
accepted output variable formats) and Tables 5 through 8
(which list valid elements for two-terminal, three- or
four-terminal devices, transmission line devices, and AC
specifications).
Table 4
PSpice output variable formats
Format
Meaning
V[ac](< +
V[ac](<
out id >)
+out id >,< - out id >)
voltage at out
id
voltage across + and -
out id’s
V[ac](<
2-terminal device out id >)
voltage at a 2-terminal
device out id
V[ac](<
>) or
3 or 4-terminal device out id
voltage at
non-grounded terminal
x of a 3 or 4-terminal
V<x >[ac](< 3
>)
or 4-terminal out device
V<x ><y >[ac](< 3 or 4-terminal out
device >)
V[ac](<
transmission line out id >) or
V<z >[ac](< transmission line out
device >)
device
voltage across terminals
x and y of a
3 or 4-terminal
device
voltage at one end z of a
transmission line
device
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Chapter 7 Setting up analyses and starting simulation
Table 4
PSpice output variable formats (continued)
Format
Meaning
I[ac](< 3 or 4-terminal
>:<x >) or
I<x >[ac](<
>)
3 or 4-terminal out device
I[ac](< transmission
>:<z >) or
I<z >[ac](<
>)
< DC
out device
line out device
3 or 4-terminal out device
sweep variable >
Table 5
current through
non-grounded terminal
x of a 3 or 4-terminal
out device
current through one end
z of a transmission
line out device
voltage or current
source name
Element definitions for 2-terminal devices
Device type
< out id > or
< out device >
device indicator
Output variable
examples
capacitor
C
V(CAP:1)
I(CAP)
diode
D
V(D23:1)
I(D23)
voltage-controlled
voltage source
E
current-controlled
current source
F
voltage-controlled
current source
G
current-controlled
voltage source
H
independent current
source
I
inductor
L
V(E14:1)
I(E14)
V(F1:1)
I(F1)
V(G2:1)
I(G2)
V(HSOURCE:1)
I(HSOURCE)
V(IDRIV:+)
I(IDRIV)
V(L1:1)
I(L1)
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Setting up analyses
Table 5
Element definitions for 2-terminal devices
Device type
< out id > or
< out device >
device indicator
Output variable
examples
resistor
R
V(RC1:1)
I(RC1)
voltage-controlled
switch
S
independent voltage
source
V
current-controlled
switch
W
Table 6
V(SWITCH:+)
I(SWITCH)
V(VSRC:+)
I(VSRC)
V(W22:-)
I(W22)
Element definitions for 3- or 4-terminal devices
Device type
< out
or
< out
id >
device >
<pin id >
Output variable
examples
D (Drain terminal)
V(B11:D)
G (Gate terminal)
ID(B11)
device
indicator
GaAs MESFET
B
S (Source terminal)
Junction FET
J
D (Drain terminal)
VG(JFET)
G (Gate terminal)
I(JFET:G)
S (Source terminal)
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Chapter 7 Setting up analyses and starting simulation
Table 6
Element definitions for 3- or 4-terminal devices
Device type
< out
or
< out
id >
device >
<pin id >
Output variable
examples
device
indicator
MOSFET
M
B (Bulk, substrate
terminal)
VDG(M1)
ID(M1)
D (Drain terminal)
G (Gate terminal)
S (Source terminal)
bipolar
transistor
Q
B (Base terminal)
V(Q1:B)
C (Collector terminal)
I(Q1:C)
E (Emitter terminal)
S (Source terminal)
IGBT
Z
C (Collector terminal)
V(Z1:C)
E (Emitter terminal)
I(Z1:C)
G (Gate terminal)
Table 7
Element definitions for transmission line devices
Device type
transmission
line
204
< out id > or
< out device >
device indicator
<z >
Output variable
examples
T
A (Port A)
V(T32:A+)
B (Port B)
I(T32:B-)
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Setting up analyses
Table 8
Element definitions for AC analysis specific elements
<ac suffix >
device symbol
Meaning
Output variable
examples
(none)
magnitude (default)
V(V1)
I(V1)
M
magnitude
VM(CAP1:1)
IM(CAP1:1)
DB
magnitude in decibels
VDB(R1)
P
phase
IP(R1)
R
real part
VR(R1)
I
imaginary part
VI(R1)
The INOISE, ONOISE, DB(INOISE), and DB(ONOISE)
output variables are predefined for use with noise (AC
sweep) analysis.
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Chapter 7 Setting up analyses and starting simulation
Starting a simulation
After you have used Capture to enter your circuit design
and have set up the analyses to be performed, you can
start a simulation by choosing Run from the PSpice menu.
When you enter and set up your circuit this way, Capture
automatically generates the simulation files and starts
PSpice.
There may be situations, however, when you want to run
PSpice outside of Capture. You may want to simulate a
circuit that was not created in Capture, for example, or
you may want to run simulations of multiple circuits in
batch mode.
This section includes the following:
•
Starting a simulation from Capture, below
•
Starting a simulation outside of Capture on page 7-207
•
Setting up batch simulations on page 7-207
•
The PSpice simulation window on page 7-208
Starting a simulation from Capture
After you have set up the analyses for the circuit, you can
start a simulation from Capture in either of the following
ways:
206
•
From the PSpice menu select Run.
•
Click the Simulate button on the PSpice toolbar.
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Starting a simulation
Starting a simulation outside of Capture
To start PSpice outside of Capture
1
From the Start menu, point to the OrCAD program
group, then choose PSpice.
2
From the File menu, choose Open Simulation.
3
Do one of the following:
•
Double-click on the simulation profile filename
(*.SIM) in the list box.
•
Enter the simulation profile filename (*.SIM) in the
File name text box and click Open.
4
From the Simulation menu, choose Edit Settings to
modify any of the analysis setup parameters.
5
From the Simulation menu, choose Run (or click the
Run toolbar button) to begin the simulation.
Setting up batch simulations
Multiple simulations can be run in batch mode when
starting PSpice directly with circuit file input. You can use
batch mode, for example, to run a number of simulations
overnight. There are two ways to do this, as described
below.
Multiple simulation setups within one circuit file
Multiple circuit/simulation descriptions can be
concatenated into a single circuit file and simulated all at
once with PSpice. Each circuit/simulation description in
the file must begin with a title line and end with a .END
statement.
The simulator reads all the circuits in the circuit file and
then processes each one in sequence. The data file and
simulation output file contain the outputs from each
circuit in the same order as they appeared in the circuit
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Chapter 7 Setting up analyses and starting simulation
file. The effect is the same as if you had run each circuit
separately and then concatenated all of the outputs.
Running simulations with multiple circuit files
You can direct PSpice to simulate multiple circuit files
using either of the following methods.
Method 1
1
From the Start menu, point to the OrCAD program
group, then choose PSpice.
2
Select Open Simulation from the File menu from the
PSpice window.
3
Do one of the following:
•
Type each file name in the File Name text box
separated by a space.
•
Use the combination keystrokes and mouse clicks
in the list box as follows: C+click to select file
names one at a time, and V+click to select groups
of files.
Method 2
1
From the Start menu, point to the OrCAD program
group, then choose PSpice.
2
Update the command line in the following way:
•
Include a list of circuit file names separated by
spaces.
Circuit file names can be fully qualified or can contain
the wild card characters (* and ?).
The PSpice simulation window
The PSpice Simulation Window is an MDI (Multiple
Document Interface) application. This implies that you
can open and display multiple files at the same time in this
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Starting a simulation
window. For instance, you can have a waveform file
(.DAT), a circuit file (.CIR), and a simulation output file
(.OUT) open and displayed in different child windows
within this one window.
The PSpice Simulation Window consists of three sections:
the main window section where the open files are
displayed, the output window section where output
information such as informational, warning, and error
messages from the simulator are shown, and the
simulation status window section where detailed status
information about the simulation are shown. These three
sections are shown in Figure 56.
The windows in these sections may be resized, moved,
and reordered as needed.
The simulation window also includes a menu bar and
toolbars for controlling the simulation and the waveform
display.
Title bar
The title bar of the simulation window (the
area at the top of the window) identifies the name of the
currently open simulation (either simulation profile or
circuit file) and the name of the currently active document
displayed in the main window area. For example, the
simulation window shown in Figure 56 indicates that
simulation profile Example-TRAN is currently open and
the active document displayed is
Example-Example-TRAN.DAT.
Menus and Toolbars The menus accessed from the
menu bar include commands to set up and control the
simulator, customize the window display characteristics,
and configure the way the waveforms are displayed. The
toolbar buttons duplicate many of the more frequently
used commands.
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Chapter 7 Setting up analyses and starting simulation
Figure 55 PSpice simulation window
Main window section The top central portion (by
default) of the simulation window is the main window
section where documents (such as waveforms, circuit
description, output information etc.) are displayed within
child windows. These windows are tabbed by default.
The tabs at the bottom left show the names of the
documents that each child window contains. Clicking on
a tab brings that child window to the foreground. Figure
56 shows the tabbed document windows for
Example-Example-TRAN.DAT and
Example-Example-TRAN.OUT.
You can configure the display of these windows to suit
your preferences and to make the analysis of the circuit
quick and readily understandable. These windows can
also be resized, moved, and reordered to suit your needs.
Output window section
The lower left portion of the
simulation window provides a listing of the output from
the simulation. It shows informational, warning, and
error messages from the simulation. You can resize and
relocate this window to make it easier to read.
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Starting a simulation
Simulation status window section
The lower right
portion of the simulation window presents a set of tabbed
windows that show detailed status about the simulation.
There are three tabbed windows in this section: the
Analysis window, the Watch Variable window, and the
Devices window. The Analysis window provides a
running log of values of simulation variables (parameters
such as Temperature, Time Step, and Time). The Watch
Variable window displays watch variables and their
values. These are the variables setup to be monitored
during simulation. The Devices window displays the
devices that are being simulated.
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Chapter 7 Setting up analyses and starting simulation
212
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DC analyses
8
Chapter overview
This chapter describes how to set up DC analyses and
includes the following sections:
•
DC Sweep on page 8-214
•
Bias point on page 8-223
•
Small-signal DC transfer on page 8-225
•
DC sensitivity on page 8-228
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Chapter 8 DC analyses
DC Sweep
Minimum requirements to run a DC sweep analysis
Minimum circuit design requirements
Table 9
214
DC sweep circuit design requirements
Swept variable type
Requirement
voltage source
voltage source with a DC specification
(VDC, for example)
temperature
none
current source
current source with a DC specification
(IDC, for example)
model parameter
PSpice model (.MODEL)
global parameter
global parameter defined with a
parameter block (.PARAM)
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DC Sweep
Minimum program setup requirements
1
In Capture, select New Simulation Profile or Edit
Simulation Settings from the PSpice menu. (If this is a
new simulation, enter the name of the profile and click
OK.)
The Simulation Settings dialog box appears.
2
Under Analysis type, select DC Sweep.
3
For the Primary Sweep option, enter the necessary
parameter values and select the appropriate check
boxes to complete the analysis specifications.
4
Click OK to save the simulation profile.
5
Select Run under the PSpice menu to start the
simulation.
Note
Do not specify a DC sweep and a parametric analysis for the same
variable.
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Chapter 8 DC analyses
Overview of DC sweep
The DC sweep analysis causes a DC sweep to be
performed on the circuit. DC sweep allows you to sweep
a source (voltage or current), a global parameter, a model
parameter, or the temperature through a range of values.
The bias point of the circuit is calculated for each value of
the sweep. This is useful for finding the transfer function
of an amplifier, the high and low thresholds of a logic gate,
and so on.
For the DC sweep analysis specified in Figure 56, the
voltage source V1 is swept from -0.125 volts to 0.125 volts
by steps of 0.005. This means that the output has
(0.125 + 0.125)/0.005 +1 = 51 steps or simulation points.
A source with a DC specification (such as VDC or IDC)
must be used if the swept variable is to be a voltage type
or current source. To set the DC value, select Properties
from the Edit menu, then click on the cell under the DC
column and type in its value.
The default DC value of V1 is overridden during the DC
sweep analysis and is made to be the swept value. All of
the other sources retain their values.
After running the analysis, the simulation output file
(EXAMPLE.OUT for the EXAMPLE.OPJ circuit in
Figure 56) contains a table of voltages relating V1, node
OUT1, and node OUT2.
216
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DC Sweep
The example circuit EXAMPLE.OPJ is
provided with the OrCAD program
installation.
Figure 56 Example schematic EXAMPLE.OPJ.
To calculate the DC response of an analog circuit, PSpice
removes time from the circuit. This is done by treating all
capacitors as open circuits, all inductors as shorts, and
using only the DC values of voltage and current sources.
In order to solve the circuit equations, PSpice uses an
iterative algorithm. For analog devices, the equations are
continuous.
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Chapter 8 DC analyses
Setting up a DC stimulus
To run a DC sweep or small-signal DC transfer analysis,
you need to place and connect one or more independent
sources and then set the DC voltage or current level for
each source.
To set up a DC stimulus
1
Place and connect one of these symbols in your
schematic:
Table 10
If you are planning to run an AC or
transient analysis in addition to a DC
analysis, see the following:
For voltage input
Use this...
When you are running...
• Using time-based stimulus
VDC
A DC Sweep and/or Bias Point (transfer
function) analysis only.
VSRC
Multiple analysis types including DC
Sweep and/or Bias Point (transfer
function).
parts with AC and DC
properties on page 3-77 for
other source symbols that you can use.
• Using VSRC or ISRC parts
on page 3-78 to find out how to
specify the TRAN attribute for a
time-based input signal when using
VSRC or ISRC symbols.
218
Table 11
For current input
Use this...
When you are running...
IDC
A DC Sweep and/or Bias Point (transfer
function) analysis only.
ISRC
Multiple analysis types including DC
Sweep and/or Bias Point (transfer
function).
2
Double-click the symbol instance to display the Parts
spreadsheet appears.
3
Click in the cell under the DC column to edit its value.
4
Define the DC specification as follows:
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DC Sweep
Table 12
Set this attribute...
To this value...
DC
DC_level
where DC_level is in volts or amps
(units are optional).
5
Click OK twice to exit the dialog boxes.
Nested DC sweeps
A second sweep variable can be selected after a primary
sweep value has been specified in the DC Sweep dialog
box. When you specify a secondary sweep variable, it
forms the outer loop for the analysis. That is, for every
increment of the second sweep variable, the first sweep
variable is stepped through its entire range of values.
To set up a nested sweep
1
Under Options, select the Secondary Sweep box for
the DC Sweep Analysis type.
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Chapter 8 DC analyses
2
220
Enter the necessary parameter values and select the
appropriate check boxes to complete the analysis
specifications.
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DC Sweep
Curve families for DC sweeps
When a nested DC sweep is performed, the entire curve
family is displayed. That is, the nested DC sweep is
treated as a single data section (or you can think of it as a
single PSpice run).
For the circuit shown in Figure 57, you can set up a DC
sweep analysis with an outer sweep of the voltage source
VD and an inner sweep of the voltage source VG as listed
in Table 1.
Table 1
Curve family example setup
Outer sweep
Nested sweep
Swept Var Type
voltage source
voltage source
Sweep Type
linear
linear
Name
VD
VG
Start Value
0
0
End Value
5
2
Increment
0.1
0.5
When the DC sweep analysis is run, add a current marker
at the drain pin of M1 and display the simulation results
in PSpice. The result will look like Figure 58.
To add a load line for a resistor, add a trace that computes
the load line from the sweep voltage. Assume that the X
axis variable is the sweep voltage V_VD, which runs from
0 to 5 volts. The expression which will add a trace that is
the load line for a 50 kohm resistor is:
Figure 57 Curve family example
schematic.
In Capture, from the PSpice menu, point to
Markers, then choose Mark Current Into Pin
to add a current marker.
V_VD is the hierarchical name for VD
created by netlisting the schematic.
(5V-V_VD)/50K
This can be useful for determining the bias point for each
member of a curve family as shown in Figure 59.
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Chapter 8 DC analyses
Figure 58 Device curve family.
Figure 59 Operating point determination for each member of the
curve family.
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Bias point
Bias point
Minimum requirements to run a bias point analysis
Minimum circuit design requirements
None.
Minimum program setup requirements
1
Under Analysis type in the Simulation Settings dialog
box, select Bias Point.
2
For the General Settings option, enter the necessary
parameter values and select the appropriate check
boxes to complete the analysis specifications.
3
Click OK to save the simulation profile.
4
In Capture, from the PSpice menu, select Run to start
the simulation.
Overview of bias point
The bias point is calculated for any analysis whether or
not the Bias Point analysis is enabled in the Simulation
Settings dialog box. However, additional information is
reported when the Bias Point analysis is enabled.
Also see Save and load bias point
on page A-374.
When Bias Point analysis is not enabled, only analog node
voltages and states are reported to the output file.
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Chapter 8 DC analyses
When the Bias Point analysis is enabled, the following
information is reported to the output file:
•
a list of all analog node voltages
•
the currents of all voltage sources and their total
power
•
a list of the small-signal parameters for all devices
If Bias Point is enabled, you can suppress the reporting of
the bias point analog node values, as follows:
224
1
Under the Options tab in the Simulation Settings
dialog box, select Output file in the Category box.
2
Uncheck the box for Bias point node voltages
(NOBIAS).
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Small-signal DC transfer
Small-signal DC transfer
Minimum requirements to run a small-signal DC
transfer analysis
Minimum circuit design requirements
•
The circuit should contain an input source, such as
VSRC.
Minimum program setup requirements
1
Under Analysis type in the Simulation Settings dialog
box, select Bias Point.
2
Specify the name of the input source desired. See
Output variables on page 7-199 for a description of
output variable formats.
3
Click OK to save the simulation profile.
4
In Capture, from the PSpice menu, select Run to start
the simulation.
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Chapter 8 DC analyses
Overview of small-signal DC transfer
The small-signal DC transfer analysis calculates the
small-signal transfer function by transforming the circuit
around the bias point and treating it as a linear circuit .
The small-signal gain, input resistance, and output
resistance are calculated and reported.
For N and O devices in the analog interface subcircuits,
has a well-defined linear equivalent.
To calculate the small-signal gain, input resistance, and output
resistance
1
In the Bias Point dialog box, select Calculate
small-signal DC gain (.TF).
2
Specify the value for either an output voltage or the
current through a voltage source in the To Output
variable box.
For example, entering V(a,b) as the output variable
specifies that the output variable is the output voltage
between two nets, a and b. Entering I(VDRIV) as the
output variable specifies that the output variable is the
current through a voltage source VDRIV.
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Small-signal DC transfer
3
Specify the input source name in the Calculate
small-signal DC gain (.TF) portion of the Bias Point
dialog box.
The gain from the input source to the output variable
is calculated along with the input and output
resistances.
For example, if you enter V(OUT2) as the output
variable and V1 as the input source, the input
resistance for V1 is calculated, the output resistance
for V(OUT2) is calculated, and the gain from V1 to
V(OUT2) is calculated. All calculations are reported to
the simulation output file.
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Chapter 8 DC analyses
DC sensitivity
Minimum requirements to run a DC sensitivity
analysis
Minimum circuit design requirements
None.
Minimum program setup requirements
228
1
In the Bias Point dialog box, select Perform Sensitivity
analysis (.SENS).
2
Enter the required value(s) in the Output variable(s)
box.
3
Click OK to save the simulation profile. (Be sure you
give the new profile an appropriate name under the
General tab prior to saving.)
4
In Capture, from the PSpice menu, select Run to start
the simulation.
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DC sensitivity
Overview of DC sensitivity
DC sensitivity analysis calculates and reports the
sensitivity of one node voltage to each device parameter
for the following device types:
•
resistors
•
independent voltage and current sources
•
voltage and current-controlled switches
•
diodes
•
bipolar transistors
The sensitivity is calculated by linearizing all devices
around the bias point.
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Chapter 8 DC analyses
230
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AC analyses
9
Chapter overview
This chapter describes how to set up AC sweep and noise
analyses.
•
AC sweep analysis on page 9-232 describes how to set up
an analysis to calculate the frequency response of your
circuit. This section also discusses how to define an
AC stimulus and how PSpice treats nonlinear devices
in an AC sweep.
•
Noise analysis on page 9-241 describes how to set up an
analysis to calculate device noise contributions and
total input and output noise.
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Chapter 9 AC analyses
AC sweep analysis
Setting up and running an AC sweep
The following procedure describes the minimum setup
requirements for running an AC sweep analysis. For more
detail on any step, go to the pages referenced in the
sidebars.
To set up and run an AC sweep
To find out how, see Setting up an AC
stimulus on page 9-233.
1
Place and connect a voltage or current source with an
AC input signal.
2
From the PSpice menu, select New Simulation Profile
or Edit Simulation Settings. (If this is a new
simulation, enter the name of the profile and click
OK.)
The Simulation Settings dialog box appears.
To find out how, see Setting up an AC
analysis on page 9-235.
3
Choose AC Sweep/Noise in the Analysis type list box.
4
Specify the required parameters for the AC sweep or
noise analysis you want to run.
5
Click OK to save the simulation profile.
6
From the PSpice menu, select Run to start the
simulation.
What is AC sweep?
To find out more, see How PSpice
treats nonlinear devices on
page 9-239.
232
AC sweep is a frequency response analysis. PSpice
calculates the small-signal response of the circuit to a
combination of inputs by transforming it around the bias
point and treating it as a linear circuit. Here are a few
things to note:
•
Nonlinear devices, such as voltage- or
current-controlled switches, are transformed to linear
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AC sweep analysis
circuits about their bias point value before PSpice runs
the linear (small-signal) analysis.
•
Because AC sweep analysis is a linear analysis, it only
considers the gain and phase response of the circuit; it
does not limit voltages or currents.
The best way to use AC sweep analysis is to set the source
magnitude to one. This way, the measured output equals
the gain, relative to the input source, at that output.
Setting up an AC stimulus
To run an AC sweep analysis, you need to place and
connect one or more independent sources and then set the
AC magnitude and phase for each source.
To set up an AC stimulus
1
Place and connect one of these symbols in your
schematic:
Note Unlike DC sweep, the AC
Sweep/Noise dialog box not include an
input source option. Instead, each
independent source in your circuit contains
its own AC specification for magnitude and
phase.
Table 2
For voltage input
Use this...
When you are running...
VAC
An AC sweep analysis only.
VSRC
Multiple analysis types including AC
sweep.
If you are planning to run a DC or transient
analysis in addition to an AC analysis, see
If you want to specify multiple
stimulus types on page 3-77 for
additional information and source symbols
that you can use.
Table 3
For current input
2
Use this...
When you are running...
IAC
An AC sweep analysis only.
ISRC
Multiple analysis types including AC
sweep.
Double-click the symbol instance to display the Parts
spreadsheet.
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Chapter 9 AC analyses
3
Click in the cell under the appropriate property
column to edit its value. Depending on the source
symbol that you placed, define the AC specification as
follows:
Table 4
For VAC or IAC
Set this property...
To this value...
ACMAG
AC magnitude in volts (for VAC) or
amps (for IAC); units are optional.
ACPHASE
Optional AC phase in degrees.
Table 5
For VSRC or ISRC
If you are also planning to run a transient
analysis, see Using VSRC or ISRC
parts on page 3-78 to find out how to
specify the TRAN property.
234
Set this property...
To this value...
AC
Magnitude_value [phase_value]
where magnitude_value is in volts or
amps (units are optional) and the
optional phase_value is in degrees.
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AC sweep analysis
Setting up an AC analysis
To set up the AC analysis
1
From the PSpice menu, choose New Simulation
Profile or Edit Simulation Settings. (If this is a new
simulation, enter the name of the profile and click
OK.)
The Simulation Settings dialog box appears.
2
Choose AC Sweep/Noise in the Analysis type list box.
3
Under Options, select General Settings if it is not
already enabled.
4
Set the number of sweep points as follows:
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Chapter 9 AC analyses
Table 6
If you also want to run a noise analysis,
then before clicking OK, complete the Noise
Analysis frame in this dialog box as
described in Setting up a noise
analysis on page 9-243.
236
To sweep frequency...
Do this...
linearly
Under AC Sweep Type, click
Linear, and enter the total number
of points in the sweep in the Total
Points box.
logarithmically by
decades
Under AC Sweep Type, click
Logarithmic, select Decade
(default), and enter the total
number of points per decade in the
Total Points box.
logarithmically by
octaves
Under AC Sweep Type, click
Logarithmic, select Octave, and
enter the total number of points
per octave in the Total Points box.
5
In the Start Frequency and End Frequency text boxes,
enter the starting and ending frequencies,
respectively, for the sweep.
6
Click OK to save the simulation profile.
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AC sweep analysis
AC sweep setup in example.opj
If you look at the example circuit, EXAMPLE.OPJ,
provided with your OrCAD programs, you’ll find that its
AC analysis is set up as shown in Figure 61.
Note The source, V1, is a VSIN source that
is normally used for setting up sine wave
signals for a transient analysis. It also has
an AC property so that you can use it for an
AC analysis.
To find out more about VSIN and other
source symbols that you can use for AC
analysis, see Using time-based
stimulus parts with AC and DC
properties on page 3-77.
Figure 60 Circuit diagram for EXAMPLE.OPJ.
Frequency is swept from 100 kHz to 10 GHz by decades,
with 10 points per decade. The V1 independent voltage
source is the only input to an amplifier, so it is the only AC
stimulus to this circuit. Magnitude equals 1 V and relative
phase is left at zero degrees (the default). All other voltage
sources have zero AC value.
237
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Chapter 9 AC analyses
Note The source, V1, is a VSIN source that
is normally used for setting up sine wave
signals for a transient analysis. It also has
an AC property so that you can use it for an
AC analysis.
To find out more about VSIN and other
source symbols that you can use for AC
analysis, see Using time-based
stimulus parts with AC and DC
properties on page 3-77.
Figure 61 AC analysis setup for EXAMPLE.OPJ.
Frequency is swept from 100 kHz to 10 GHz by decades,
with 10 points per decade. The V1 independent voltage
source is the only input to an amplifier, so it is the only AC
stimulus to this circuit. Magnitude equals 1 V and relative
phase is left at zero degrees (the default). All other voltage
sources have zero AC value.
238
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AC sweep analysis
How PSpice treats nonlinear devices
An AC Sweep analysis is a linear or small-signal analysis.
This means that nonlinear devices must be linearized to
run the analysis.
What’s required to transform a device into a linear
circuit
In order to transform a device (such as a transistor
amplifier) into a linear circuit, you must do the following:
1
Compute the DC bias point for the circuit.
2
Compute the complex impedance and/or
transconductance values for each device at this bias
point.
3
Perform the linear circuit analysis at the frequencies of
interest by using simplifying approximations.
What PSpice does
Example: Replace a bipolar transistor in
common-emitter mode with a constant
transconductance (collector current
proportional to base-emitter voltage) and a
number of constant impedances.
PSpice automates this process for you. PSpice computes
the partial derivatives for nonlinear devices at the bias
point and uses these to perform small-signal analysis.
Example: nonlinear behavioral modeling block
Suppose you have an analog behavioral modeling block
that multiplies V(1) by V(2). Multiplication is a nonlinear
operation. To run an AC sweep analysis on this block, the
block needs to be replaced with its linear equivalent. To
determine the linear equivalent block, PSpice needs a
known bias point.
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Chapter 9 AC analyses
Using a DC source
Consider the circuit shown here. At the DC bias point,
PSpice calculates the partial derivatives which determine
the linear response of the multiplier as follows:
∂V ( Out )
∂V ( Out )
V ( Out ) = V ( In1 ) ⋅ ---------------------- + V ( In2 ) ⋅ ---------------------∂V ( In1 )
∂V ( In2 )
= V ( In1 ) ⋅ V ( In2 ) + V ( In2 ) ⋅ V ( In1 )
For this circuit, this equation reduces to:
V ( Out ) = V ( In1 ) ⋅ 2 + V ( In2 ) ⋅ 0
This means that the multiplier acts as an amplifier of the
AC input with a gain that is set by the DC input.
Caution: multiplying AC sources
This is exactly how a double-balanced
mixer behaves. In practice, this is a simple
multiplier.
Note A double-balanced mixer with inputs
at the same frequency would produce
outputs at DC at twice the input frequency,
but these terms cannot be seen with a
linear, small-signal analysis.
240
Suppose that you replace the 2 volt DC source in this
example with an AC source with amplitude 1 and no DC
value (DC=0). When PSpice computes the bias point, there
are no DC sources in the circuit, so all nodes are at 0 volts
at the bias point. The linear equivalent of the multiplier
block is a block with gain 0, which means that there is no
output voltage at the fundamental frequency.
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Noise analysis
Noise analysis
Setting up and running a noise analysis
The following procedure describes the minimum setup
requirements for running a noise analysis. For more detail
on any step, go to the pages referenced in the sidebars.
To set up and run an AC sweep
1
Place and connect a voltage or current source with an
AC input signal.
To find out how, see Setting up an AC
stimulus on page 9-233.
2
Set up the AC sweep simulation specifications.
3
Set up the noise simulation specifications and enable
the analysis in the AC Sweep/Noise portion of the
Simulation Settings dialog box.
To find out how, see Setting up an AC
analysis on page 9-235.
To find out how, see Setting up a noise
analysis on page 9-243.
4
Click OK to save the simulation profile.
5
From the PSpice menu, choose Run to start the
simulation.
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Chapter 9 AC analyses
What is noise analysis?
When running a noise analysis, PSpice calculates and
reports the following for each frequency specified for the
AC Sweep/Noise analysis:
•
Device noise, which is the noise contribution
propagated to the specified output net from every
resistor and semiconductor device in the circuit; for
semiconductor devices, the device noise is also broken
down into constituent noise contributions where
applicable
•
Total output and equivalent input noise
Example: Diodes have separate noise
contributions from thermal, shot, and
flicker noise.
Table 7
This value...
Means this...
Output noise
RMS sum of all the device contributions
propagated to a specified output net
Input noise
equivalent noise that would be needed
at the input source to generate the
calculated output noise in an ideal
(noiseless) circuit
How PSpice calculates total output
and input noise
To calculate total noise at an output net, PSpice computes
the RMS sum of the noise propagated to the net by all
noise-generating devices in the circuit.
To calculate the equivalent input noise, PSpice then
divides total output noise by the gain from the input
source to the output net. This results in the amount of
noise which, if injected at the input source into a noiseless
circuit, would produce the total noise originally
calculated for the output net.
242
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Noise analysis
Setting up a noise analysis
To set up the noise analysis
1
From the PSpice menu, choose New Simulation
Profile or Edit Simulation Settings. (If this is a new
simulation, enter the name of the profile and click
OK.)
The Simulation Settings dialog box appears.
2
Choose AC Sweep/Noise in the Analysis type list box.
3
Under Options, select General Settings if it is not
already enabled.
4
Specify the AC sweep analysis parameters as
described on page 9-235.
5
Enable the Noise Analysis check box.
6
Enter the noise analysis parameters as follows:
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Chapter 9 AC analyses
Table 8
To find out more about valid syntax, see
Output variables on page 7-199.
In this text box...
Type this...
Output Voltage
A voltage output variable of the
form V(node, [node]) where you
want the total output noise
calculated.
I/V Source
The name of an independent current
or voltage source where you want
the equivalent input noise
calculated.
Note If the source is in a lower level of
a hierarchical schematic, separate the
names of the hierarchical devices with
periods (.).
Example: U1.V2
Note In the Probe window, you can view
the device noise contributions at every
frequency specified in the AC sweep. The
Interval parameter has no effect on what
PSpice writes to the Probe data file.
Interval
7
244
An integer n designating that at
every nth frequency, you want to see
a table printed in the PSpice output
file (.out) showing the individual
contributions of all of the circuit’s
noise generators to the total noise.
Click OK to save the simulation profile.
Pspug.book Page 245 Wednesday, November 11, 1998 1:14 PM
Noise analysis
Analyzing Noise in the Probe window
You can use these output variable formats to view traces
for device noise contributions and total input or output
noise at every frequency in the analysis.
For a break down of noise output variables
by supported device type, see Table 6
on page 13-358.
To view this...
Use this output variable...
Which is represented by this equation*...
Flicker noise for a device
NFID(device_name)
NFIB(device_name)
noise ∝ k f ⋅ ----b-
Shot noise for a device
NSID(device_name)
NSIB(device_name)
NSIC(device_name)
For diodes and BJTs:
I
af
f
noise ∝ 2qI
For GaAsFETs, JFETs, and
MOSFETs:
dI 2
- ⋅ --noise ∝ 4k T ⋅ -----dV 3
Thermal noise for the RB, RC, RD,
RE, RG, or RS constituent of a
device, respectively
NRB(device_name)
NRC(device_name)
NRD(device_name)
NRE(device_name)
NRG(device_name)
NRS(device_name)
noise ∝ ----------
Total noise for a device
NTOT(device_name)
Sum of all contributors in
4k T
R
device_name
Total output noise for the circuit
NTOT(ONOISE)
∑
N T OT ( dev ice )
dev ice
RMS-summed output noise for the
circuit
V(ONOISE)
Equivalent input noise for the
circuit
V(INOISE)
RMS sum of all contributors
( N T OT ( ON OIS E ) )
V ( ON OIS E )
--------------------------------gain
* To find out more about the equations that describe noise behavior, refer to the appropriate device type in the A nalog
Devices chapter in the OrCAD PSpice Reference Manual.
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Chapter 9 AC analyses
About noise units
Table 9
This type of noise output variable...
Is reported in these units...
Device contribution of the form
Nxxx
( v olts ) ⁄ ( Hz )
Total input or output noise of the
form V(ONOISE) or V(INOISE)
( v olts ) ⁄ ( Hz )
2
Example
You can run a noise analysis on the circuit shown in
Figure 60 on page 9-237.
To run a noise analysis on the example:
In Capture, open the EXAMPLE.DSN circuit provided
with your OrCAD programs in the
ORCAD\CAPTURE\SAMPLES subdirectory.
1
From the PSpice menu, choose New Simulation
Profile or Edit Simulation Settings. (If this is a new
simulation, enter the name of the profile and click
OK.)
The Simulation Settings dialog box appears.
For a description of the Interval parameter,
see page 9-244.
246
2
Choose AC Sweep/Noise in the Analysis type list box.
3
Under Options, select General Settings if it is not
already enabled.
4
Enable the Noise Analysis check box.
5
Enter the following parameters for the noise analysis:
Output Voltage
V(OUT2)
I/V Source
V1
Interval
30
These settings mean that PSpice will calculate noise
contributions and total output noise at net OUT2 and
equivalent input noise from V1.
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Noise analysis
Figure 63 shows Probe traces for Q1’s constituent noise
sources as well as total nose for the circuit after
simulating. Notice that the trace for RMSSUM (at the top
of the plot), which is a macro for the trace expression
SQRT(NTOT(Q1) + NTOT(Q2) + NTOT(Q3) + ... ),
To find out more about PSpice macros,
refer to PSpice A/D online Help.
exactly matches the total output noise, V(ONOISE),
calculated by PSpice.
Note The source, V1, is a VSIN source that
is normally used for setting up sine wave
signals for a transient analysis. It also has
an AC property so that you can use it for an
AC analysis.
To find out more about VSIN and other
source symbols that you can use for AC
analysis, see Using time-based
stimulus parts with AC and DC
properties on page 3-77.
Figure 62 Device and total noise traces for EXAMPLE.DSN.
Frequency is swept from 100 kHz to 10 GHz by decades,
with 10 points per decade. The V1 independent voltage
source is the only input to an amplifier, so it is the only AC
stimulus to this circuit. Magnitude equals 1 V and relative
phase is left at zero degrees (the default). All other voltage
sources have zero AC value.
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Chapter 9 AC analyses
248
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Transient analysis
10
Chapter overview
This chapter describes how to set up a transient analysis
and includes the following sections:
•
Overview of transient analysis on page 10-250
•
Defining a time-based stimulus on page 10-252
•
Transient (time) response on page 10-263
•
Internal time steps in transient analyses on page 10-265
•
Switching circuits in transient analyses on page 10-266
•
Plotting hysteresis curves on page 10-266
•
Fourier components on page 10-268
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Chapter 10 Transient analysis
Overview of transient analysis
Minimum requirements to run a transient analysis
Minimum circuit design requirements
Circuit should contain one of the following:
•
An independent source with a transient specification
(see Table 10)
•
An initial condition on a reactive element
•
A controlled source that is a function of time
Minimum program setup requirements
See Setting up analyses on
page 7-197 for a description of the
Analysis Setup dialog box.
1
From the PSpice menu, choose New Simulation
Profile or Edit Simulation Settings. (If this is a new
simulation, enter the name of the profile and click
OK.)
The Simulation Settings dialog box appears.
250
2
From the Analysis type list box, select Time Domain
(Transient).
3
Specify the required parameters for the transient
analysis you want to run.
4
Click OK to save the simulation profile.
5
From the PSpice menu, choose Run to start the
simulation.
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Overview of transient analysis
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Chapter 10 Transient analysis
Defining a time-based stimulus
Overview of stimulus generation
Symbols that generate input signals for your circuit can be
divided into two categories:
•
those whose transient behavior is characterized
graphically using the Stimulus Editor
•
those whose transient behavior is characterized by
manually defining their properties within Capture
Their symbols are summarized in Table 10.
Table 10
252
Stimulus symbols for time-based input signals
Specified by...
Symbol name
Description
Using the
Stimulus Editor
VSTIM
voltage source
ISTIM
current source
Defining symbol
attribute
VSRC
VEXP
VPULSE
VPWL
VPWL_RE_FOREVER
VPWL_F_RE_FOREVER
VPWL_N_TIMES
VPWL_F_N_TIMES
VSFFM
VSIN
voltage sources
ISRC
IEXP
IPULSE
IPWL
IPWL_RE_FOREVER
IPWL_F_RE_FOREVER
IPWL_N_TIMES
IPWL_F_N_TIMES
ISFFM
ISIN
current sources
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The Stimulus Editor utility
To use any of these source types, you must place the
symbol in your schematic and then define its transient
behavior.
Each property-characterized stimulus has a distinct set of
attributes depending upon the kind of transient behavior
it represents. For VPWL_F_xxx, IPWL_F_xxx, and FSTIM,
a separate file contains the stimulus specification.
As an alternative, the Stimulus Editor utility automates
the process of defining the transient behavior of stimulus
devices. The Stimulus Editor allows you to create analog
stimuli which generate sine wave, repeating pulse,
exponential pulse, single-frequency FM, and piecewise
linear waveforms.
The stimulus specification created using the Stimulus
Editor is saved to a file, automatically configured into the
schematic, and associated with the corresponding VSTIM
or ISTIM part instance or symbol definition.
The Stimulus Editor utility
The Stimulus Editor is a utility that allows you to quickly
set up and verify the input waveforms for a transient
analysis. You can create and edit voltage sources, and
current sources for your circuit. Menu prompts guide you
to provide the necessary parameters, such as the rise time,
fall time, and period of an analog repeating pulse.
Graphical feedback allows you quickly verify the
waveform.
OrCAD program versions without the
Stimulus Editor must use the
characterized-by-property sources listed in
Table 10 on page 10-252.
Stimulus files
The Stimulus Editor produces a file containing the stimuli
with their transient specification. These stimuli are
defined as simulator device declarations using the V
(voltage source) and I (current source) forms. Since the
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Chapter 10 Transient analysis
Stimulus Editor produces these statements automatically,
you will never have to be concerned with their syntax.
However, if you are interested in a detailed description of
their syntax, see the descriptions of V and I devices in the
A nalog Devices chapter of the the online OrCA D PSpice A /D
Reference Manual.
Configuring stimulus files
The Include Files tab in the Simulation Settings dialog box
allows you to view the list of stimulus files pertaining to
your current schematic. You can also manually add,
delete, or change the stimulus file configuration in this tab
dialog box. The list box displays all of the currently
configured stimulus files. One file is specified per line.
Files can be configured as either global to the Capture
environment or local to the current design. Global files are
marked with an asterisk (*) after the file name.
When starting the Stimulus Editor from Capture, stimulus
files are automatically configured (added to the list) as
local to the current design. Otherwise, new stimulus files
can be added to the list by entering the file name in the
Filename text box and then clicking the Add to design
(local configuration) or Add as global (global
configuration) button.
Starting the Stimulus Editor
The Stimulus Editor is fully integrated with Capture and
can be run from either the schematic editor or symbol
editor.
You can start the Stimulus Editor by doing the following:
254
6
Select one or more stimulus instances in the schematic
7
From the Edit menu, choose PSpice Stimulus.
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The Stimulus Editor utility
When you first start the Stimulus Editor, you may need to
adjust the scale settings to fit the trace you are going to
add. You can use Axis Settings on the Plot menu or the
corresponding toolbar button to change the displayed
data, the extent of the scrolling region, and the minimum
resolution for each of the axes. Displayed Data Range
parameters determine what portion of the stimulus data
set will be presented on the screen. Extent of Scrolling
Region parameters set the absolute limits on the viewable
range. Minimum Resolution parameters determine the
smallest usable increment (example: if it is set to 1 msec,
then you cannot add a data point at 1.5 msec).
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Chapter 10 Transient analysis
Defining stimuli
1
Place stimulus part instances from the symbol set:
VSTIM, ISTIM and DIGSTIMn.
2
Click the source instance to select it.
3
From the Edit menu, choose PSpice Stimulus to start
the Stimulus Editor.
4
Fill in the transient specification according to the
dialogs and prompts.
5
From the File menu, choose Save to save the edits.
Example: piecewise linear stimulus
256
1
Open an existing schematic or start a new one.
2
From the Place menu, choose Part and browse the
SOURCE.OLB part library file for VSTIM (and select
it).
3
Place the part. It looks like a regular voltage source
with an implementation property displayed.
4
Click the implementation label and type Vfirst. This
names the stimulus that you are going to create.
5
If you are working in a new schematic, use Save from
the File menu to save it. This is necessary since the
schematic name is used to create the default stimulus
file name.
6
Click the VSTIM part to select it.
7
From the Edit menu, choose PSpice Stimulus. This
starts the Stimulus Editor and displays the New
Stimulus dialog box. You can see that the stimulus
already has the name of Vfirst.
8
Select PWL in the dialog box and click OK. The cursor
looks like a pencil. The message in the status bar at the
bottom of the screen lets you know that you are in the
process of adding new data points to the stimulus. The
left end of the bottom status bar displays the current
coordinates of the cursor.
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The Stimulus Editor utility
9
Move the cursor to (200ns, 1) and click the left mouse
button. This adds the point. Notice that there is
automatically a point at (0,0). Ignore it for now and
continue to add a couple more points to the right of the
current one.
10 Click-right to stop adding points.
11 From the File menu, choose Save.
If you make a mistake or want to make any changes,
reshape the trace by dragging any of the handles to a new
location. The dragged handle cannot pass any other
defined data point.
To delete a point, click its handle and press X.
To add additional points, either choose Add Point from
the Edit menu, press A+A, or click the Add Point
toolbar button.
At this point you can return to Capture, edit the current
stimulus, or go on to create another.
Example: sine wave sweep
1
Open an existing schematic or start a new one.
2
Place a VSTIM part on your schematic.
3
To name the stimulus, double-click the
implementation property and type Vsin.
4
Click the VSTIM part to select it.
5
From the PSpice menu, choose Edit Stimulus to start
the Stimulus Editor.
6
Define the stimulus parameter for amplitude:
a
From the New Stimulus dialog box, choose Cancel.
b
From the Tools menu, choose Parameters.
c
Enter AMP=1 in the Definition text box, and click
OK.
d
From the Stimulus menu, choose New or click the
New Stimulus button in the toolbar.
This example creates a 10 k sine wave with
the amplitude parameterized so that it can
be swept during a simulation.
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Chapter 10 Transient analysis
7
8
9
e
Give the stimulus the name of Vsin.
f
Select SIN as the type of stimulus to be created,
and click OK.
Define the other stimulus properties:
a
Enter 0 for Offset Value.
b
Enter {AMP} for Amplitude. The curly braces are
required. They indicate that the expression needs
to be evaluated at simulation time.
c
Enter 10k for Frequency and click OK.
d
From the File menu, choose Save.
Within Capture, place and define the PARAM symbol:
a
From the Place menu, choose Part.
b
Either browse SPECIAL.OLB for the PARAM part
or type in the name.
c
Place the part on your schematic and double-click
it.
d
Click New to add a new user property.
e
Set the value property name to AMP (no curly
braces).
f
Set the value of the VALUE1 property to 1.
Set up the parametric sweep and other analyses:
a
From the PSpice menu, choose Stimulus Editor,
and click the Parametric Sweep button.
b
Select Global Parameter in the Swept Var. Type
frame.
c
Select Linear in the Sweep type frame.
10 Enter AMP in the Name text box.
11 Specify values for the Start Value, End Value, and
Increment text boxes.
You can now set up your usual Transient, AC, or DC
analysis and run the simulation.
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The Stimulus Editor utility
Creating new stimulus symbols
1
Use the Capture part editor to edit or create a part with
the following properties:
Implementation Type
PSpice Stimulus
Implementation
name of the stimulus model
STIMTYPE
type of stimulus; valid values
are ANALOG; if this property
is nonexistent, the stimulus is
assumed to be ANALOG
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Chapter 10 Transient analysis
Editing a stimulus
To edit an existing stimulus
PWL stimuli are a little different since they
are a series of time/value pairs.
This provides a fast way to scale a PWL
stimulus.
260
1
Start the Stimulus Editor and select Get from the
Stimulus menu.
2
Double-click the trace name (at the bottom of the X
axis for analog). This opens the Stimulus Attributes
dialog box where you can modify the attributes of the
stimulus directly and immediately see the effect of the
changes.
To edit a PWL stimulus
1
Double click the trace name. This displays the handles
for each defined data point.
2
Click any handle to select it. To reshape the trace, drag
it to a new location. To delete the data point, press X.
3
To add additional data points, either select Add from
the Edit menu or click the Add Point button.
4
Right-click to end adding new points.
To select a time and value scale factor for PWL
stimuli
1
Select the PWL trace by clicking on its name.
2
Select Attributes from the Edit menu or click the
corresponding toolbar button.
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The Stimulus Editor utility
Deleting and removing traces
To delete a trace from the displayed screen, select the trace
name by clicking on its name, then press X. This will
only erase the display of the trace, not delete it from your
file. The trace is still available by selecting Get from the
Stimulus menu.
To remove a trace from a file, select Remove from the
Stimulus menu.
Once a trace is removed, it is no longer retrievable. Delete traces
with caution.
Note
Manual stimulus configuration
Stimuli can be characterized by manually starting the
Stimulus Editor and saving their specifications to a file.
These stimulus specifications can then be associated to
stimulus instances in your schematic or to stimulus
symbols in the symbol library.
To manually configure a stimulus
1
Start the Stimulus Editor by double-clicking on the
Stimulus Editor icon in the OrCAD program group.
2
Open a stimulus file by selecting Open from the File
menu. If the file is not found in your current library
search path, you are prompted for a new file name.
3
Create one or more stimuli to be used in your
schematic. For each stimulus:
a
Name it whatever you want. This name will be
used to associate the stimulus specification to the
stimulus instance in your schematic, or to the
symbol in the symbol library.
b
Provide the transient specification.
c
From the File menu, choose Save.
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Chapter 10 Transient analysis
4
In the schematic page editor, configure the Stimulus
Editor’s output file into your schematic:
a
From the Pspice menu, choose Edit Simulation
Settings.
a
In the Simulation Settings dialog box, select the
Include Files tab.
b
Enter the file name specified in step 2.
c
If the stimulus specifications are for local use in the
current design, click the Add to design button. For
global use by any design, use Add as global
instead.
d
Click OK.
5
Modify either the stimulus instances in the schematic
or symbols in the symbol library to reference the new
stimulus specification.
6
Associate the transient stimulus specification to a
stimulus instance:
a
Place a stimulus part in your schematic from the
part set: VSTIM, ISTIM, and DIGSTIMn.
b
Click the VSTIM, ISTIM, or DIGSTIMn instance.
c
From the Edit menu, choose Properties.
d
Click the Implementation cell, type in the name of
the stimulus, and click Apply.
e
Complete specification of any VSTIM or ISTIM
instances by selecting Properties from the Edit
menu and editing their DC and AC attributes.
Click the DC cell and type its value.
Click the AC cell, type its value, and then click
Apply.
f
7
262
Close the property editor spreadsheet.
To change stimulus references globally for a part:
a
Select the part you want to edit.
a
From the Edit menu, choose Part to start the part
editor.
Pspug.book Page 263 Wednesday, November 11, 1998 1:14 PM
Transient (time) response
b
Create or change the part definition, making sure
to define the following properties:
Implementation
stimulus name as defined in
the Stimulus Editor
See Chapter 5, Creating parts for
models, for a description of how to create
and edit parts.
Transient (time) response
The Transient response analysis causes the response of the
circuit to be calculated from TIME = 0 to a specified time.
A transient analysis specification is shown for the circuit
EXAMPLE.OPJ in Figure 63. (EXAMPLE.OPJ is shown in
Figure 64.)
The analysis is to span the time interval from 0 to 1000
nanoseconds and values should be reported to the
simulation output file every 20 nanoseconds.
Figure 63 Transient analysis setup for EXAMPLE.OPJ.
263
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Chapter 10 Transient analysis
During a transient analysis, any or all of the independent
sources may have time-varying values. In EXAMPLE.OPJ,
the only source which has a time-varying value is V1
(VSIN part) with attributes:
VOFF = 0v
VAMPL = 0.1v
FREQ = 5Meg
V1’s value varies as a 5 MHz sine wave with an offset
voltage of 0 volts and a peak amplitude of 0.1 volts. In
general, more than one source has time-varying values.
The example circuit EXAMPLE.OPJ is
provided with the OrCAD program
installation.
Figure 64 Example schematic EXAMPLE.OPJ.
The transient analysis does its own calculation of a bias
point to start with, using the same technique as described
for DC sweep. This is necessary because the initial values
of the sources can be different from their DC values. To
report the small-signal parameters for the transient bias
point, use the Transient command and enable Detailed
Bias Point. Otherwise, if you simply want the result of the
transient run itself, you should only enable the Transient
command.
In the simulation output file EXAMPLE.OUT, the
bias-point report for the transient bias point is labeled
INITIAL TRANSIENT SOLUTION.
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Internal time steps in transient analyses
Internal time steps in transient
analyses
During analog analysis, PSpice maintains an internal time
step which is continuously adjusted to maintain accuracy
while not performing unnecessary steps. During periods
of inactivity, the internal time step is increased. During
active regions, it is decreased. The maximum internal step
size can be controlled by specifying it in the Step Ceiling
text box in the Transient dialog box. PSpice will never
exceed either the step ceiling value or two percent of the
total transient run time, whichever is less.
The internal time steps used may not correspond to the
time steps at which information has been requested to be
reported. The values at the print time steps are obtained
by second-order polynomial interpolation from values at
the internal steps.
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Chapter 10 Transient analysis
Switching circuits in transient
analyses
Running transient analysis on switching circuits can lead
to long run times. PSpice must keep the internal time step
short compared to the switching period, but the circuit’s
response extends over many switching cycles.
This technique is described in:
V. Bello, “Computer Program Adds SPICE to
Switching-Regulator Analysis,”
Electronic Design, March 5, 1981.
One method of avoiding this problem is to transform the
switching circuit into an equivalent circuit without
switching. The equivalent circuit represents a sort of quasi
steady-state of the actual circuit and can correctly model
the actual circuit’s response as long as the inputs do not
change too fast.
Plotting hysteresis curves
Transient analysis can be used to look at a circuit’s
hysteresis. Consider, for instance, the circuit shown in
Figure 65 (netlist in Figure 66).
Figure 65 ECL-compatible Schmitt trigger.
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Plotting hysteresis curves
* Capture Netlist
R_RIN
1 2 50
R_RC1
0 3 50
R_R1
3 5 185
R_R2
5 8 760
R_RC2
0 6 100
R_RE
4 8 260
R_RTH2
7 0 85
C_CLOAD 0 7 5PF
V_VEE
8 0 dc -5
V_VIN
1 0
+PWL 0 -8 1MS -1.0V 2MS -1.8V
R_RTH1
8 7 125
Q_Q1
3 2 4 QSTD
Q_Q2
6 5 4 QSTD
Q_Q3
0 6 7 QSTD
Q_Q4
0 6 7 QSTD
Figure 66 Netlist for Schmitt trigger circuit.
The QSTD model is defined as:
.MODEL QSTD NPN( is=1e-16 bf=50 br=0.1 rb=50 rc=10
tf=.12ns tr=5ns
+ cje=.4pF pe=.8 me=.4 cjc=.5pF pc=.8 mc=.333 ccs=1pF
va=50)
Instead of using the DC sweep to look at the hysteresis,
use the transient analysis, (Print Step = .01ms and Final
Time = 2ms) sweeping VIN from -1.8 volts to -1.0 volts
and back down to -1.8 volts, very slowly. This has two
advantages:
•
it avoids convergence problems
•
it covers both the upward and downward transitions
in one analysis
After the simulation, in the Probe window in PSpice , the
X axis variable is initially set to be Time. By selecting
X Axis Settings from the Plot menu and clicking on the
Axis Variable button, you can set the X axis variable to be
V(1). Then use Add on the Trace menu to display V(7),
and change the X axis to a user defined data range from
-1.8V to -1.0V (Axis Settings on the Plot menu). This plots
the output of the Schmitt trigger against its input, which is
the desired outcome. The result looks similar to Figure 67.
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Chapter 10 Transient analysis
Figure 67 Hysteresis curve example: Schmitt trigger.
Fourier components
Note You must do a transient analysis
in order to do a Fourier analysis. The
sampling interval used during the
Fourier transform is equal to the print
step specified for the transient analysis.
Fourier analysis is enabled through the Output File
Options dialog box under the Time Domain (Transient)
Analysis type. Fourier analysis calculates the DC and
Fourier components of the result of a transient analysis.
By default, the first through ninth components are
computed; however, more can be specified.
When selecting Fourier to run a harmonic decomposition
analysis on a transient waveform, only a portion of the
waveform is used. Using the Probe window in PSpice , a
Fast Fourier Transform (FFT) of the complete waveform
can be calculated and its spectrum displayed.
In the example shown in Figure 63 on page 10-263, the
voltage waveform at node OUT2 from the transient
analysis is to be used and the fundamental frequency is to
be one megahertz for the harmonic decomposition. The
period of fundamental frequency is one microsecond
(inverse of the fundamental frequency). Only the last one
microsecond of the transient analysis is used, and that
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Fourier components
portion is assumed to repeat indefinitely. Since V1’s sine
wave does indeed repeat every one microsecond, this is
sufficient. In general, however, you must make sure that
the fundamental Fourier period fits the waveform in the
transient analysis.
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Chapter 10 Transient analysis
270
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Parametric and temperature
analysis
11
Chapter overview
This chapter describes how to set up parametric and
temperature analyses. Parametric and temperature are
both simple multi-run analysis types.
This chapter includes the following sections:
•
Parametric analysis on page 11-272
•
Temperature analysis on page 11-281
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Chapter 11 Parametric and temperature analysis
Parametric analysis
Minimum requirements to run a parametric
analysis
Minimum circuit design requirements
•
Set up the circuit according to the swept variable type
as listed in Table 1.
•
Set up a DC sweep, AC sweep, or transient analysis.
Table 1
Parametric analysis circuit design requirements
Swept variable type
Requirement
voltage source
voltage source with a DC specification
(VDC, for example)
temperature
none
current source
current source with a DC specification
(IDC, for example)
model parameter
PSpice model
global parameter
global parameter defined with a
parameter block (PARAM)
Minimum program setup requirements
See Setting up analyses on
page 7-197 for a description of the
Simulation Settings dialog box.
272
1
In the Simulation Settings dialog box, from the
Analysis type list box, select Time Domain (Transient).
2
Under Options, select Parametric Sweep if it is not
already enabled.
3
Specify the required parameters for the sweep.
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Parametric analysis
4
Click OK to save the simulation profile.
5
From the PSpice menu, choose Run to start the
simulation.
Note
Do not specify a DC sweep and a parametric analysis for the same
variable.
Overview of parametric analysis
Parametric analysis performs multiple iterations of a
specified standard analysis while varying a global
parameter, model parameter, component value, or
operational temperature. The effect is the same as running
the circuit several times, once for each value of the swept
variable.
See Parametric analysis on page 2-42 for a description of how
to set up a parametric analysis.
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Chapter 11 Parametric and temperature analysis
RLC filter example
This example shows how to perform a parametric sweep
and analyze the results with performance analysis.
Use performance analysis to derive values from a series of
simulator runs and plot these values versus a parameter
that varies between the simulator runs.
For this example, the derived values are the overshoot and
the rise time versus the damping resistance of the filter.
Entering the design
The schematic representation for the RLC filter
(RLCFILT.OPJ) is shown in Figure 68.
Figure 68 Passive filter schematic.
This series of PSpice runs varies the value of resistor R1
from 0.5 to 1.5 ohms in 0.1 ohm steps. Since the
time-constant of the circuit is about one second, perform a
transient analysis of approximately 20 seconds.
Create the circuit in OrCAD Capture by placing a
piecewise linear independent current source (IPWL from
SOURCE.OLB). Set the current source properties as
follows:
AC
T1
I1
T2
274
=
=
=
=
1a
0s
0a
10ms
Pspug.book Page 275 Wednesday, November 11, 1998 1:14 PM
Parametric analysis
I2 = 0a
T3 = 10.1ms
I3 = 1a
Place an instance of a resistor and set its VALUE property
to the expression, {R}. To define R as a global parameter,
place a PARAM pseudocomponent and use the Property
Editor to create a new property R and set its value to 0.5.
Place an inductor and set its value to 1H, place a capacitor
and set its value to 1, and place an analog ground symbol
(0 from SOURCE.OLB). Wire the schematic symbols
together as shown in Figure 68.
Running the simulation
Run PSpice with the following analyses enabled:
transient
print step:
final time:
100ms
20s
parametric
swept var. type:
sweep type:
name:
start value:
end value:
increment:
global parameter
linear
R
0.5
1.5
0.1
After setting up the analyses, start the simulation by
choosing Run from the PSpice menu.
Using performance analysis to plot overshoot and
rise time
After performing the simulation that creates the data file
RLCFILT.DAT, you can calcualte the specified
performance analysis goal functions.
When the simulation is finished, a list appears containing
all of the sections (runs) in the data file produced by
PSpice. To use the data from every run, select All and click
OK in the Available Selections dialog box. In the case of
Figure 69, the trace I(L1) from the ninth section was added
by specifying the following in the Add Traces dialog box:
To display the Add Traces dialog box, from
the Trace menu, choose Add Trace or click
the Add Trace toolbar button.
I(L1)@9
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Chapter 11 Parametric and temperature analysis
Troubleshooting tip
More than one PSpice run or data section is
required for performance analysis. Because
one data value is derived for each
waveform in a related set of waveforms, at
least two data points are required to
produce a trace.
Use Eval Goal Function (from the Trace
menu) to evaluate a goal function on a
single waveform and produce a single data
point result.
Figure 69 Current of L1 when R1 is 1.5 ohms.
To run performance analysis
1
From the Trace menu, choose Performance Analysis .
2
Click OK.
PSpice resets the X-axis variable for the graph to be the
parameter that changed between PSpice runs. In the
example, this is the R parameter.
To see the rise time for the current through the inductor
L1, click the Add Trace toolbar button and then enter:
genrise( I(L1) )
The genrise and overshoot goal functions
are contained in the file PSPICE.PRB in the
OrCAD directory.
Figure 70, shows how the rise time decreases as the
damping resistance increases for the filter.
Another Y axis can be added to the plot for the overshoot
of the current through L1 by selecting Add Y Axis from
the Plot menu. The Y axis is immediately added. Now
click the Add Trace toolbar button and enter:
overshoot( I(L1) )
Figure 70 shows how the overshoot increases with
increasing resistance.
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Parametric analysis
Figure 70 Rise time and overshoot vs. damping resistance.
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Chapter 11 Parametric and temperature analysis
Example: frequency response vs. arbitrary
parameter
This technique for measuring branch
capacitances works well in both simple and
complex circuits.
You can view a plot of the linear response of a circuit at a
specific frequency as one of the circuit parameters varies
(such as the output of a band pass filter at its center
frequency vs. an inductor value).
In this example, the value of a nonlinear capacitance is
measured using a 10 kHz AC signal and plotted versus its
bias voltage. The capacitance is in parallel with a resistor,
so a trace expression is used to calculate the capacitance
from the complex admittance of the R-C pair.
Setting up the circuit
Enter the circuit in Capture as shown in Figure 71
To create the capacitor model in the schematic editor:
Figure 71 RLC filter example circuit.
1
Place a CBREAK part.
2
Select it so that it is highlighted.
3
From the Edit menu, choose PSpice Model.
4
In the Model Text frame, enter the following:
.model Cnln CAP(C=1 VC1=-0.01 VC2=0.05)
5
From the File menu, choose Save.
Set up the circuit for a parametric AC analysis (sweep
Vbias), and run PSpice. Include only the frequency of
interest in the AC sweep.
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Parametric analysis
To display the results
Use PSpice to display the capacitance calculated at the
frequency of interest versus the stepped parameter.
1
Simulate the circuit.
2
Load all AC analysis sections.
3
From the Trace menu, choose Add Trace or click the
Add Trace toolbar button.
4
Add the following trace expression:
IMG(-I(Vin)/V(1,0))/(2*3.1416*Frequency)
Or add the expression:
CvF(-I(Vin)/V(1,0))
Where CvF is a macro which measures the effective
capacitance in a complex conductance. Macros are defined
using the Macros command on the Trace menu. The CvF
macro should be defined as:
CvF(G)= IMG(G)/(2*3.1416*Frequency)
Note
-I(Vin)/V(1) is the complex admittance of the R-C branch; the
minus sign is required for correct polarity.
To use performance analysis to plot capacitance vs. bias voltage
1
From the Trace menu, choose Performance Analysis.
2
Click Wizard.
3
Click Next>.
4
Click YatX in the Choose a Goal Function list, and then
click Next>.
5
In the Name of Trace text box, type the following:
CvF(-I(Vin)/V(1))
6
In the X value to get Y value at text box, type 10K.
7
Click Next>.
The wizard displays the gain trace for the first run to
text the goal function (YatX).
8
Click Finish.
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Chapter 11 Parametric and temperature analysis
The resultant plot is shown in Figure 72.
Figure 72 Plot of capacitance versus bias voltage.
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Temperature analysis
Temperature analysis
Minimum requirements to run a temperature
analysis
Minimum circuit design requirements
None.
Minimum program setup requirements
1
In the Simulation Settings dialog box, from the
Analysis type list box, select Time Domain (Transient).
2
Under Options, select Temperature Sweep if it is not
already enabled.
3
Specify the required parameters for the sweep.
4
Click OK to save the simulation profile.
5
From the PSpice menu, choose Run to start the
simulation.
See Setting up analyses on
page 7-197 for a description of the
Simulation Settings dialog box.
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Chapter 11 Parametric and temperature analysis
Overview of temperature analysis
Running multiple analyses for different
temperatures can also be achieved using
parametric analysis (see Parametric
analysis on page 11-272). With
parametric analysis, the temperatures can
be specified either by list, or by range and
increments within the range.
For a temperature analysis, PSpice reruns standard
analyses set in the Simulation Settings dialog box at
different temperatures.
You can specify zero or more temperatures. If no
temperature is specified, the circuit is run at 27°C. If more
than one temperature is listed, the simulation runs once
for each temperature in the list.
Setting the temperature to a value other than the default
results in recalculating the values of
temperature-dependent devices. In EXAMPLE.OPJ (see
Figure 73), the temperature for all of the analyses is set to
35°C. The values for resistors RC1 and RC2 are
recomputed based upon the CRES model which has
parameters TC1 and TC2 reflecting linear and quadratic
temperature dependencies.
Likewise, the Q3 and Q4 device values are recomputed
using the Q2N2222 model which also has
temperature-dependent parameters. In the simulation
output file, these recomputed device values are reported
in the section labeled TEMPERATURE ADJUSTED
VALUES.
The example circuit EXAMPLE.OPJ is
provided with the OrCAD program
installation.
Figure 73 Example schematic EXAMPLE.OPJ.
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Monte Carlo and sensitivity/
worst-case analyses
12
Chapter overview
This chapter describes how to set up Monte Carlo and
sensitivity/worst-case analyses and includes the
following sections:
•
Statistical analyses on page 12-284
•
Monte Carlo analysis on page 12-289
•
Worst-case analysis on page 12-306
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Statistical analyses
Monte Carlo and sensitivity/worst-case are statistical
analyses. This section describes information common to
both types of analyses.
See Monte Carlo analysis on page 12-289 for information
specific to Monte Carlo analyses, and see Worst-case
analysis on page 12-306 for information specific to
sensitivity/worst-case analyses.
Overview of statistical analyses
Generating statistical results
As the number of Monte Carlo or worst-case
runs increases, simulation takes longer and
the data file gets larger. Large data files
may be slow to open and slow to draw
traces.
One way to work around this is to set up an
overnight batch job to run the simulation
and execute commands. You can even set
up the batch job to produce a series of plots
on paper to be ready for you in the
morning.
The Monte Carlo and worst-case analyses vary the lot or
device tolerances of devices between multiple runs of an
analysis (DC, AC, or transient). Before running the
analysis, you must set up the model and/or lot tolerances
of the model parameter to be investigated.
A Monte Carlo analysis performs a Monte Carlo
(statistical) analysis of the circuit. A worst-case analysis
performs a sensitivity and worst-case analysis of the
circuit.
Sensitivity/worst-case analyses are different from Monte
Carlo analyses in that they compute the parameters using
the sensitivity data rather than using random numbers.
You can run either a Monte Carlo or a worst-case analysis,
but you cannot run both at the same time. Multiple runs of
the selected analysis are done while parameters are
varied. You can select only one analysis type (AC, DC, or
transient) per run. The selected analysis is repeated in
subsequent passes of the analysis.
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Statistical analyses
Output control for statistical analyses
Monte Carlo and sensitivity/worst-case analyses
generate the following types of reports:
•
Model parameter values used for each run (that is, the
values with tolerances applied)
•
Waveforms from each run, as a function of specifying
data collection, or by specifying output variables in
the analysis set up
•
Summary of all the runs using a collating function
Output is saved to the data file for use by the waveform
analyzer. For Monte Carlo analyses, you can use the
performance analysis feature to produce histograms of
derived data.
For information about performance
analysis, see RLC filter example on
page 11-274.
For information about histograms, see
Creating histograms on
page 12-303.
Model parameter values reports
To produce a list of the model parameters actually used
for each run,
1
In the Simulation Settings dialog box, click the
Analysis tab.
2
From the Analysis type list, select an analysis type.
3
Under Options, select Monte Carlo/Worst Case.
4
Click the More Settings button.
5
Select List model parameter values.
6
Click OK to close the Simulation Settings dialog box.
This list is written to the simulation output file at the
beginning of the run and contains the parameters for each
device, as opposed to the parameters for each .MODEL
statement. This is because devices can have different
parameter values when using a model statement
containing a DEV tolerance.
Note that for midsize and large circuits, the List option can
produce a large output file.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Waveform reports
For Monte Carlo analyses, there are five variations of the
output that you can specify in the Save data from text box
on the Monte Carlo dialog box. Options:
In excess of about 10 runs, the waveform
display can look more like a band than a
set of individual waveforms. This can be
useful for seeing the typical spread for a
particular output variable. As the number
of runs increases, the spread more closely
approximates the actual worst-case limits
for the circuit.
<none>
No output is generated
All
Forces all output to be generated
(including nominal run)
First*
Generates output only during the first
n runs
Every*
Generates output for every nth run
Runs(list)*
Does specified analysis and generates
outputs only for the listed runs (up to
25 values can be specified in the list)
The * indicates that you can set the number of runs in the
runs text box.
Values for the output variables specified in the selected
analyses are saved to the simulation output file and data
file.
Note
286
Even a modest number of runs can produce large output files.
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Statistical analyses
Collating functions
You can further compress the results of Monte Carlo and
worst-case analyses. If you use the collating function, a
single number represents each run. (Click the Output File
Options button and select a function from the Find list.) A
table of deviations per run is reported in the simulation
output file.
Collating functions are listed in Table 1.
Table 1
Collating functions used in statistical analyses
Function
Description
YMAX
Find the greatest difference in each
waveform from the nominal
MAX
Find the maximum value of each waveform
MIN
Find the minimum value of each waveform
RISE_EDGE
Find the first occurrence of the waveform
crossing above a specified threshold value
FALL_EDGE
Find the first occurrence of the waveform
crossing below a specified threshold value
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Temperature considerations in statistical analyses
Refer to Temperature Effects on
Monte Carlo A nalysis in the
A pplication Notes manual for more
information.
The statistical analyses perform multiple runs, as does the
temperature analysis. Conceptually, the Monte Carlo and
worst-case loops are inside the temperature loop.
However, since both temperature and tolerances affect the
model parameters, OrCAD recommends not using
temperature analysis when using Monte Carlo or
worst-case analysis.
Also, you cannot sweep the temperature in a DC sweep
analysis or put tolerances on temperature coefficients
while performing one of these statistical analyses. In
EXAMPLE.DSN, the temperature value is fixed at 35 ° C.
The example schematic EXAMPLE.DSN is
provided on the OrCAD installation CD.
Figure 74 Example schematic EXAMPLE.DSN.
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Monte Carlo analysis
Monte Carlo analysis
The Monte Carlo analysis calculates the circuit response to
changes in part values by randomly varying all of the
model parameters for which a tolerance is specified. This
provides statistical data on the impact of a device
parameter’s variance.
With Monte Carlo analysis, model parameters are given
tolerances, and multiple analyses (DC, AC, or transient)
are run using these tolerances.
Monte Carlo analysis is frequently used to
predict yields on production runs of a
circuit.
For EXAMPLE.DSN in Figure 74 on page 12-288, you can
analyze the effects of variances in the values of resistors
RC1 and RC2 by assigning a model description to these
resistors that includes a 5% device tolerance on the
multiplier parameter R.
Then you can perform a Monte Carlo analysis. First, the
simulator performs a DC analysis with the nominal R
multiplier value for RC1 and RC2. Then it performs a set
number of additional runs with the R multiplier varied
independently for RC1 and RC2 within a 5% tolerance.
To modify example.dsn and set up simulation
1
Replace RC1 and RC2 with RBREAK parts, setting
property values to match the resistors that are being
replaced (VALUE=10k) and reference designators to
match previous names.
2
Select PSpice Model from the Edit menu. Create the
model CRES as follows:
.MODEL CRES RES( R=1 DEV=5% TC1=0.02
+ TC2=0.0045 )
From the File menu, choose Save. By default, Capture
saves the definition to the model library
EXAMPLE.LIB and automatically configures the file
for local use with the current schematic.
3
TC1 is the linear temperature coefficient.
TC2 is the quadratic temperature
coefficient.
In Capture, set up a new Monte Carlo analysis as
shown in Figure 75. The analysis specification tells
PSpice to do one nominal run and four Monte Carlo
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
runs, saving the DC analysis output from those five
runs.
Figure 75 Monte Carlo analysis setup for EXAMPLE.DSN.
PSpice starts by running all of the analyses enabled in the
Simulation Settings dialog box with all parameters set to
their nominal values.
PSpice offers a facility to generate
histograms of data derived from Monte
Carlo waveform families through the
performance analysis feature.
For information about performance
analysis, see RLC filter example on
page 11-274.
For information about histograms, see
Creating histograms on
page 12-303.
290
However, with Monte Carlo enabled, PSpice saves the DC
sweep analysis results for later reference and comparison.
After the nominal analyses are finished, PSpice performs
the additional specified analysis runs (in this example, DC
sweep).
Subsequent runs use the same analysis specification as the
nominal run with one major exception: instead of using
the nominal parameter values, the tolerances are applied
to set new parameter values and thus, new part values.
There is a trade-off in choosing the number of Monte
Carlo runs. More runs provide better statistics, but they
require more time. The amount of time scales directly with
the number of runs: 20 transient analyses take 20 times as
long as one transient analysis. During Monte Carlo runs,
the PSpice status display includes the current run number
and the total number of runs left.
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Monte Carlo analysis
Reading the summary report
The summary report generated in this example (see
Figure 76) specifies that the waveform generated from
V(OUT1, OUT2) should be the subject of the collating
function YMAX. In each of the last four runs, the new
V(OUT1, OUT2) waveform is compared to the nominal
V(OUT1, OUT2) waveform for the first run, calculating
the maximum deviation in the Y direction (YMAX
collating function). The deviations are printed in order of
size along with their run number .
Figure 76 Summary of Monte Carlo runs for EXAMPLE.OPJ.
With the List option enabled, a report is also generated
showing the parameter value used for each device in each
run. In this case (see Figure 77), run three shows the
highest deviation.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Figure 77 Parameter values for Monte Carlo pass three.
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Monte Carlo analysis
Example: Monte Carlo analysis of a pressure sensor
This example shows how the performance of a pressure
sensor circuit with a pressure-dependent resistor bridge is
affected by manufacturing tolerances, using Monte Carlo
analysis to explore these effects.
Drawing the schematic
To begin, construct the bridge as shown in Figure 78.
Figure 78 Pressure sensor circuit.
Here are a few things to know when placing and
connecting the part:
•
To get the part you want to place, from the Place
menu, choose Part.
•
To rotate a part before placing it, press R.
•
For V1 and Meter, place a generic voltage source using
the VSRC part. When you place the source for the
meter, change its name by double-clicking the part
and typing Meter in the Reference cell in the Parts
Spreadsheet.
•
For R1-R7, place a resistor using the R part.
•
Place the analog ground using the 0 ground symbol.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
S+W
•
To connect the parts, from the Place menu, choose
Wire.
•
To move values or reference designators, click the
value or reference designator to select it, then drag it
to the new location.
Defining part values
Define the part values as shown in Figure 78. For the
pressure sensor, you need to do the following:
Note Because the Meter source is used to
measure current, it has no DC value and
can be left unchanged.
•
Change the resistor values for R3, R5, R6, and R7 from
their default value of 1 k.
•
Set the DC value for the V1 voltage source.
To change resistor values
1
Double-click the value for a resistor.
2
Type the new value. Depending on the resistor you are
changing, set its value to one of the following (refer to
Figure 78).
Table 1
Note The value for R3—
{1k*(1+P*Pcoeff/Pnom)}—is an
expression that represents linear
dependence of resistance on pressure. To
complete the definition for R3, you will
create and define global parameters for
Pcoeff, P, and Pnom later on in this
example
3
If you are changing
this resistor...
Type this...
R3
{1k*(1+P*Pcoeff/Pnom)}
R5
2k
R6
470
R7
25
Repeat steps 1-2 for each resistor on your schematic
page.
To set the DC value for the V1 source and make it visible
294
1
Double-click the V1 source part.
2
In the Parts Spreadsheet, click in the cell under the DC
column.
3
Type 1.35v.
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Monte Carlo analysis
4
Click the Display button.
5
In the Display Format frame, choose the Value Only
option to make the DC value (1.35v) visible on the
schematic.
6
Click OK, then click Apply to apply the changes you
have made to the part.
7
Close the Parts Spreadsheet.
Setting up the parameters
To complete the value specification for R3, define the
global parameters Pcoeff, P, and Pnom.
To define and initialize Pcoeff, P, and Pnom
1
Place a PARAM part on the schematic page.
2
Double-click the PARAM part to display the Parts
Spreadsheet.
3
For each parameter, create a new property by clicking
New and typing its name. Enter its corresponding
value by clicking in the cell under the new property
name and typing its value. Specify the parameter
name and corresponding value as follows.
Table 2
4
Property
Value
Pcoeff
-0.06
P
0
Pnom
1.0
Click Apply to save the changes you have made then
close the Parts Spreadsheet.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Using resistors with models
When PSpice runs a Monte Carlo analysis, it
uses tolerance values to determine how to
vary model parameters during the
simulation.
To explore the effects of manufacturing tolerances on the
behavior of this circuit, you set device (DEV) and (LOT)
tolerances on the model parameters for resistors R1, R2,
R3, and R4 in a later step (see page 12-297). This means
you need to use resistor parts that have model
associations.
Because R parts do not have associated models (and
therefore no model parameters), change the resistor parts
to Rbreak parts that do have models.
To replace R1, R2, R3, and R4 with the RBREAK part
296
1
Click R1 to select it.
2
Hold down the C key and click R2, R3 and R4 to add
them to the selection set.
3
Press D to delete the selection set.
4
From the Place menu, choose Part.
5
Type RBREAK in the Part text box. (If RBREAK is not
available, click the Add Library button and select
BREAKOUT.OLB to configure it for use in Capture.)
6
Click OK.
7
Manually place the RBREAK part in the circuit
diagram where R1, R2, R3 and R4 were located.
8
Double-click on each RBREAK part and change the
reference designators as desired.
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Monte Carlo analysis
Saving the design
Before editing the models for the Rbreak resistors, save
the schematic.
To save the design
1
From Capture’s File menu, choose Save.
Defining tolerances for the resistor models
This section shows how to assign device (DEV) and lot
(LOT) tolerances to the model parameters for resistors R1,
R2, R3, and R4 using the model editor.
To assign 2% device and 10% lot tolerances to the resistance
multiplier for R1
1
Select R1.
2
From the Edit menu, choose PSpice Model.
You can use the model editor to change the
.MODEL or .SUBCKT syntax for a model
definition. To find out more about the
model editor, see Editing model text
on page 4-110, or refer to the online
PSpice Reference Manual.
Capture searches the libraries for the Rbreak model
definition and makes a copy to create an instance
model.
3
4
To change the instance model name from Rbreak to
Rmonte1, do the following:
a
In the Model Text frame, double-click Rbreak.
b
Type RMonte1.
To add a 2% device tolerance and a 10% lot tolerance
to the resistance multiplier, do the following:
a
Add the following to the .MODEL statement (after
R=1):
DEV=2% LOT=10%
The model editing window should look something
like Figure 79.
5
From the File menu, choose Save.
By default, Capture saves the RMonte1 .MODEL
definition to the design_name.lib library, which is
To find out more about adding model
libraries to the configuration, see
Configuring model libraries on
page 4 120
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Figure 79 Model definition for RMonte1.
PSENSOR.LIB. Capture also automatically configures the
library for local use.
To have resistors R2 and R4 use the same tolerances as R1
1
In Capture’s schematic page editor, select R2 and R4.
2
From the Edit menu, select Properties.
3
In the R2 row, click in the cell under the
Implementation column and type RMonte1.
4
In the R4 row, click in the cell under the
Implementation column and type RMonte1.
To assign 5% device tolerance to the resistance multiplier
for R3
1
Select R3.
2
From the Edit menu, select PSpice Model.
3
In the Model Text frame, change the .MODEL
statement to:
.model RTherm RES R=1 DEV=5%
4
From the File menu, choose Save.
Your schematic page should look like Figure 80.
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Monte Carlo analysis
Setting up the analyses
This section shows how to define and enable a DC
analysis that sweeps the pressure value and a Monte Carlo
analysis that runs the DC sweep with each change to the
resistance multipliers.
To set up the DC sweep
1
In the PSpice menu, choose New Simulation Profile or
Edit Simulation Settings. (If this is a new simulation,
enter the name of the profile and click OK.)
See Setting up analyses on
page 7-197 for a description of the
Simulation Settings dialog box.
The Simulation Settings dialog box appears.
Figure 80 Pressure sensor circuit with RMonte1 and RTherm
model definitions.
2
Select DC Sweep in the Analysis type list box.
3
In the Sweep Variable frame, select Global Parameter.
4
Enter the following values:
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Table 3
In this text box...
Type this...
Parameter name
P
Start value
0
End value
5.0
Increment
0.1
To set up the Monte Carlo analysis
1
Select the Monte Carlo/Worst Case option.
2
Check Monte Carlo if it is not already selected.
3
In the Number of runs text box, type 10.
4
In the Save data from list box, select All.
5
Type I(Meter) in the Output variable text box.
6
Click OK to save the simulation profile.
Running the analysis and viewing the results
To complete setup, simulate, and view results
1
From Capture’s PSpice menu, choose Run to start the
simulation
When the simulation is complete, PSpice
automatically displays the selected waveform.
Because PSpice ran a Monte Carlo analysis, it saved
multiple runs or sections of data. These are listed in
the Available Sections dialog box.
300
2
From PSpice’s Trace menu, choose Performance
Analysis.
3
Click the Select sections button.
4
In the Available Sections dialog box, click the All
button.
5
Click OK.
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Monte Carlo analysis
6
7
Note
To display current through the Meter voltage source,
do the following:
a
From Capture’s PSpice menu, point to markers
and choose Current into Pin.
b
Place a current probe on the left-hand pin of the
Meter source.
Switch to the Probe window to see the family of curves
for I(Meter) as a function of P.
For more on analyzing Monte Carlo results in PSpice, see the next
section on Monte Carlo histograms.
Monte Carlo Histograms
You can display data derived from Monte Carlo
waveform families as histograms. This is part of the
performance analysis feature.
In this example, you simulate a fourth-order Chebyshev
active filter, running a series of 100 AC analyses while
randomly varying resistor and capacitor values for each
run. Then, having defined performance analysis goal
functions for bandwidth and center frequency, you
observe the statistical distribution of these quantities for
the 100 runs.
Another way to view the family of curves
without using schematic markers is as
follows:
1 From PSpice’s Trace menu, choose Add
Trace.
2 In the Simulation Output Variables list,
double-click I(Meter).
Monte Carlo analysis is frequently used to
predict yields on production runs of a
circuit.
For more information about performance
analysis, see RLC filter example on
page 11-274.
Chebyshev filter example
The Chebyshev filter is designed to have a 10 kHz center
frequency and a 1.5 kHz bandwidth. The schematic page
for the filter is shown in Figure 81. The stimulus
specifications for V1, V2, and V3 are:
V1: DC=-15
V2: DC=+15
V3: AC=1
The parts are rounded to the nearest available 1% resistor
and 5% capacitor value. In this example, note how the
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
bandwidth and the center frequency vary when 1%
resistors and 5% capacitors are used in the circuit.
Figure 81 Chebyshev filter.
Creating models for Monte Carlo analysis
To vary the resistors and capacitors in the filter circuit,
create models for these parts on which you can set device
tolerances for Monte Carlo analysis. The
BREAKOUT.OLB library contains generic devices for this
purpose. The resistors and capacitors in this schematic are
the Rbreak and Cbreak parts from BREAKOUT.OLB.
Using the Model Editor, modify the models for these parts
as follows:
.model RMOD RES(R=1 DEV=1%)
.model CMOD CAP(C=1 DEV=5%)
Setting up the analysis
To analyze the filter, set up both an AC analysis and a
Monte Carlo analysis. The AC analysis sweeps 50 points
per decade from 100 Hz to 1 MHz. The Monte Carlo
analysis is set to take 100 runs. The analysis type is AC and
the output variable is V(OUT).
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Monte Carlo analysis
To set up the analysis
1
From PSpice’s Trace menu, choose Performance
Analysis.
2
In the Save data from list box, choose All.
3
Click OK.
Creating histograms
Because the data file can become quite large when
running a Monte Carlo analysis, to view just the output of
the filter, you place a voltage probe at the output of the
filter.
To collect data for the marked node only
1
From the PSpice menu, choose New Simulation
Profile or Edit Simulation Settings from the PSpice
menu. (If this is a new simulation, enter the name of
the profile and click OK.)
The Simulation Settings dialog box appears.
2
On the Data Collection tab, choose the At Probes only
option.
3
Click OK.
To run the simulation and load Probe with data
1
From Capture’s PSpice menu, choose Run to start the
simulation.
When the simulation is complete, PSpice
automatically displays the selected waveform.
Because PSpice ran a Monte Carlo analysis, it saved
multiple runs or sections of data. These are listed in
the Available Sections dialog box.
2
From PSpice’s Trace menu, choose Performance
Analysis.
3
Click the Select sections button.
4
In the Available Sections dialog box, click All.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
5
Click OK.
To display a histogram for the 1 dB bandwidth
For information about performance
analysis, see RLC filter example on
page 11-274.
1
From PSpice’s Plot menu, choose Axis Settings.
2
Select the X Axis tab.
3
In the Processing Options frame, select the
Performance Analysis check box.
4
Click OK.
The histogram display appears. The Y axis is the
percent of samples.
You can also display this histogram by
using the performance analysis wizard to
display Bandwidth (VDB(OUT) , 1).
5
From the Trace menu, choose Goal Functions.
6
Choose Bandwidth.
7
Click Eval.
8
Enter VDB(OUT) in the Name of trace to search text
box.
9
Enter 1 in the db level down for bandwidth calc text
box.
10 Click OK, then click Close to view the histogram.
To change the number of histogram divisions
1
From the Tools menu, choose Options.
2
In the Number of Histogram Divisions text box,
replace 10 with 20.
3
Click OK.
The histogram for 1 dB bandwidth is shown in Figure 82.
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Monte Carlo analysis
If needed, you can turn off the statistical
data display as follows:
Figure 82 1 dB bandwidth histogram.
1 From the Tools menu, choose Options.
The statistics for the histogram are shown along the
bottom of the display. The statistics show the number of
Monte Carlo runs, the number of divisions or vertical bars
that make up the histogram, mean, sigma, minimum,
maximum, 10th percentile, median, and 90th percentile.
2 Clear the Display Statistics check box.
You can also show the distribution of the center frequency
of the filter.
To display the center frequency
1
From the Trace menu, choose Goal Functions.
2
Choose CenterFreq.
3
Click Eval.
4
Enter VDB(OUT) in the Name of trace to search text
box.
5
Enter 1 in the db level down for measurement text
box.
6
Click OK, then click Close to view the histogram.
The new histogram replaces the previous histogram. To
display both histograms at once, choose Add Plot to
Window on the Plot menu before choosing Add from the
Trace menu. The histogram of the center frequency is as
shown in Figure 83.
3 Click Save, and then OK.
Ten percent of the goal function values is
less than or equal to the 10th percentile
number, and 90% of the goal function
values is greater than or equal to that
number.
If there is more than one goal function
value that satisfies this criteria, then the
10th percentile is the midpoint of the
interval between the goal function values
that satisfy the criteria. Similarly, the
median and 90th percentile numbers
represent goal function values such that
50% and 90% (respectively) of the goal
function values are less than or equal to
those numbers.
Sigma is the standard deviation of the goal
function values.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Figure 83 Center frequency histogram.
Worst-case analysis
This section discusses the analog worst-case analysis
feature of PSpice. The information provided in this section
explains how to use worst-case analysis properly and with
realistic expectations.
Overview of worst-case analysis
Worst-case analysis is used to find the worst probable
output of a circuit or system given the restricted variance
of its parameters. For instance, if the values of R1, R2, and
R3 can vary by +10%, then the worst-case analysis
attempts to find the combination of possible resistor
values which result in the worst simulated output. As
with any other analysis, there are three important parts:
inputs, procedure, and outputs.
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Worst-case analysis
Inputs
In addition to the circuit description, you need to provide
two pieces of information:
•
the parameter tolerances
•
a definition of what worst means
You can set tolerances on any number of the parameters
that characterize a model.
The criterion for determining the worst values for the
relevant model parameters is defined in the .WC
statement as a function of any standard output variable in
a specified range of the sweep.
In a given range, reduce the measurement to a single value
by one of these five collating functions:
MAX
Maximum output variable value
MIN
Minimum output variable value
YMAX
Output variable value at the point
where it differs the most with the
nominal run
RISE_EDGE
(value)
Sweep value where the output
variable value crosses above a given
threshold value
FALL_EDGE
(value)
Sweep value where the output
variable value crosses below a given
threshold value
Y ou can define W orst as the highest (HI) or lowest (LO)
possible collating function relative to the nominal run.
You can define models for nearly all
primitive analog circuit parts, such as
resistors, capacitors, inductors, and
semiconductor devices. PSpice reads the
standard model parameter tolerance
syntax specified in the .MODEL statement.
For each model parameter, PSpice uses the
nominal, minimum, and maximum
probable values, and the DEV and/or LOT
specifiers; the probability distribution type
(such as UNIFORM or GAUSS) is ignored.
You can use analog behavioral models to
measure waveform characteristics other
than those detected by the available
collating functions, such as rise time or
slope. You can also use analog behavioral
models to incorporate several voltages and
currents into one output variable to which a
collating function may be applied. See
Chapter 6, Analog behavioral
modeling, for more information.
Procedure
To establish the initial value of the collating function,
worst-case analysis begins with a nominal run using all
model parameters at their nominal values.
Next, multiple sensitivity analyses determine the
individual effect of each model parameter on the collating
function. This is accomplished by varying model
parameters, one at a time, in consecutive simulations. The
This procedure saves time by performing
the minimum number of simulations
required to make an educated guess at the
parameter values that produce the worst
results. It also has some limitations, which
are described in the following sections.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
direction (better or worse) in which the collating function
changes with a small increase in each model parameter is
recorded.
Finally, for the worst-case run, each parameter value is
taken as far from its nominal as allowed by its tolerance,
in the direction which should cause the collating function
to be its worst (given by the HI or LO specification).
Outputs
A summary of the sensitivity analysis is printed in the
PSpice output file (.OUT). This summary shows the
percent change in the collating function corresponding to
a small change in each model parameter. If a .PROBE
statement is included in the circuit file, then the results of
the nominal and worst-case runs are saved for viewing in
the Probe window.
Caution: An important condition for
correct worst-case analysis
Worst-case analysis is not an optimization process; it does
not search for the set of parameter values that result in the
worst result.
It assumes that the worst case occurs when each
parameter has been either pushed to one of its limits or left
at its nominal value as indicated by the sensitivity
analysis. It shows the true worst-case results when the
collating function is monotonic within all tolerance
combinations.
Otherwise, there is no guarantee. Usually you cannot be
certain whether this condition is true, but insight into the
operation of the circuit may alert you to possible
anomalies.
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Worst-case analysis
Worst-case analysis example
The schematic shown in Figure 84 is for an amplifier
circuit that is a biased BJT. This circuit is used to
demonstrate how a simple worst-case analysis works. It
also shows how non-monotonic dependence of the output
on a single parameter can adversely affect the worst-case
analysis.
Because an AC (small-signal) analysis is being performed,
setting the input to unity means that the output,
Vm([OUT]), is the magnitude of the gain of the amplifier.
The only variable declared in this circuit is the resistance
of Rb2. Because the value of Rb2 determines the bias on the
BJT, it also affects the amplifier’s gain.
Figure 84 Simple biased BJT amplifier.
Figure 85 is the circuit file used to run one of the
following:
•
a parametric analysis (.STEP, shown enabled in the
circuit file) that sets the value of resistor Rb2 by
stepping model parameter R through values spanning
the specified DEV tolerance range, or
•
a worst-case analysis (shown disabled in the circuit
file) that allows PSpice to determine the worst-case
value for parameter R based upon a sensitivity
analysis.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Only one of these analyses can run in any given
simulation.
Note
The AC and worst-case analysis specifications (.AC and .WC
statements) are written so that the worst-case analysis tries to
minimize Vm([OUT]) at 100 kHz.
The netlist and circuit file in Figure 85 are set up to run
either a parametric (.STEP) or worst-case (.WC) analysis of
the specified AC analysis. These simulations demonstrate
the conditions under which worst-case analysis works
well and those that can produce misleading results when
* Worst-case analysis comparing monotonic and non-monotonic
* output with a variable parameter
.lib
***** Input signal and blocking capacitor *****
Vin In
0
ac
1
Cin In
B
1u
***** "Amplifier" *****
*
gain increases with small increase in Rb2, but
*
device saturates if Rb2 is maximized.
Vcc Vcc
0
10
Rc Vcc
C
1k
Q1 C
B
0
Q2N2222
Rb1 Vcc
B
10k
Rb2 B
0
Rbmod
720
.model Rbmod res(R=1 dev 5%)
; WC analysis results
; are correct
* .model Rbmod res(R=1.1 dev 5%)
; WC analysis misled
; by sensitivity
***** Load and blocking capacitor *****
CoutC
Out
1u
Rl Out
0
1k
* Run with either the .STEP or the .WC, but not both.
* This circuit file is currently set up to run the .STEP
* (.WC is commented out)
**** Parametric Sweep—providing plot of Vm([OUT]) vs. Rb2 ****
.STEP Res Rbmod(R)
0.8 1.2 10m
***** Worst-case analysis *****
* run once for each of the .model definitions stated above)
* WC AC Vm([Out]) min range 99k 101k list output all
.AC Lin
.probe
.end
3
90k
110k
Figure 85 Amplifier netlist and circuit file.
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Worst-case analysis
output is not monotonic with a variable parameter (see
Figure 87 and Figure 88)
For demonstration, the parametric analysis is run first,
generating the curve shown in Figure 87 and Figure 88.
This curve, derived using the YatX goal function shown in
Figure 86 illustrates the non-monotonic dependence of
gain on Rb2.
YatX(1, X_value)=y1{1|sfxv(X_value)!1;}
Figure 86 YatX Goal Function.
To do this yourself, place the goal function definition in a
PROBE.GF file in the circuit directory. Then start PSpice,
load all of the AC sweeps, set up the X axis for
performance analysis, and add the following trace:
YatX(Vm([OUT]),100k)
Next, the parametric analysis is commented out and the
worst-case analysis is enabled. Two runs are made using
the two versions of the Rbmod .MODEL statement shown
in the circuit file. The model parameter, R, is a multiplier
which is used to scale the nominal value of any resistor
referencing the Rbmod model (Rb2 in this case).
Note The YatX goal function is used on the
simulation results for the parametric sweep
(.STEP) defined in Figure 85. The resulting
curves are shown in Figure 87 and
Figure 88.
The first .MODEL statement leaves the nominal value of
Rb2 at 720 ohms. The sensitivity analysis increments R by
a small amount and checks its effect on Vm([OUT]). This
slight increase in R causes an increase in the base bias
voltage of the BJT, and increases the amplifier’s gain,
Vm([OUT]). The worst-case analysis correctly sets R to its
minimum value for the lowest possible Vm([OUT]) (see
Figure 87).
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Consider a slightly different scenario: Rb2
is set to 720 ohms so that maximizing it is
not enough to saturate the BJT, but Rb1 is
variable also. The true worst case occurs
when Rb2 is maximized and Rb1 is
minimized. Checking their individual
effects is not sufficient, even if the circuit
were simulated four times with each
resistor in turn set to its extreme values.
The second .MODEL statement scales the nominal value
of Rb2 by 1.1 to approximately 800 ohms. The gain still
increases with a small increase in R, but a larger increase
in R increases the base voltage so much that it drives the
BJT into saturation and nearly eliminates the gain. The
worst-case analysis is fooled by the sensitivity analysis
into assuming that Rb2 must be minimized to degrade the
gain, but maximizing Rb2 is much worse (see Figure 88).
Note that even an optimizer, which checks the local
gradients to determine how the parameters should be
varied, is fooled by this circuit.
Output is monotonic within the tolerance
range. Sensitivity analysis correctly points
to the minimum value.
Figure 87 Correct worst-case results.
Output is non-monotonic within the
tolerance range, thus producing incorrect
worst-case results.
Figure 88 Incorrect worst-case results.
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Worst-case analysis
Tips and other useful information
VARY BOTH, VARY DEV, and VARY LOT
When VARY BOTH is specified in the .WC statement and
a model parameter is specified with both DEV and LOT
tolerances defined, the worst-case analysis may produce
unexpected results. The sensitivity of the collating
function is only tested with respect to LOT variations of
such a parameter.
For example, during the sensitivity analysis, the
parameter is varied once affecting all devices referring to
it and its effect on the collating function is recorded. For
the worst-case analysis, the parameter is changed for all
devices by LOT + DEV in the determined direction. See
the example schematic in Figure 89 and circuit file in
Figure 90.
WCASE
VARY
BOTH
Figure 89 Schematic using VARY BOTH.
Test
Vin
1
0
10V
Rs
1
2
1K
Rwc1
2
3
Rmod
100
Rwc2
3
0
Rmod
100
.MODEL Rmod RES(R=1 LOT 10% DEV 5%)
.DC Vin
LIST
10
.WC DC
V(3)
MAX
VARY BOTH
.ENDS
LIST
OUTPUT ALL
Figure 90 Circuit file using VARY BOTH.
In this case, V(3) is maximized if:
•
Rwc1 and Rwc2 are both increased by 10% per the LOT
tolerance specification, and
•
Rwc1 is decreased by 5% and Rwc2 is increased by 5%
per the DEV tolerance specification.
The final values for Rwc1 and Rwc2 should be 105 and 115,
respectively. However, because Rwc1 and Rwc2 are varied
together during the sensitivity analysis, it is assumed that
both must be increased to their maximum for a maximum
V(3). Therefore, both are increased by 15%.
The purpose of the technique is to reduce
the number of simulations. For a more
accurate worst-case analysis, you should
first perform a worst-case analysis with
VARY LOT, manually adjust the nominal
model parameter values according to the
results, then perform another analysis with
VARY DEV specified.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
Gaussian distributions
Parameters using Gaussian distributions are changed by
3σ (three times sigma) for the worst-case analysis.
YMAX collating function
This may result in maximizing or
minimizing the output variable value over
the entire range of the sweep. This collating
function is useful when you know the
direction in which the maximum deviation
occurs.
The purpose of the YMAX collating function is often
misunderstood. This function does not try to maximize
the deviation of the output variable value from nominal.
Depending on whether HI or LO is specified, it tries to
maximize or minimize the output variable value itself at
the point where maximum deviation occurred during
sensitivity analysis.
RELTOL
During the sensitivity analysis, each parameter is varied
(multiplied) by 1+RELTOL where RELTOL is specified in
a .OPTIONS statement, or defaults to 0.001.
Sensitivity analysis
The sensitivity analysis results are printed in the output
file (.OUT). For each varied parameter, the percent change
in the collating function and the sweep variable value at
which the collating function was measured are given. The
parameters are listed in worst output order; for example,
the collating function was its worst when the first
parameter printed in the list was varied.
When you use the YMAX collating function, the output
file also lists mean deviation and sigma values. These are
based on the changes in the output variable from nominal
at every sweep point in every sensitivity run.
Manual optimization
You can use worst-case analysis to perform manual
optimization with PSpice. The monotonicity condition is
usually met if the parameters have a very limited range.
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Worst-case analysis
Performing worst-case analysis with tight tolerances on
the parameters produces sensitivity and worst-case
results (in the output file). You can use these to decide
how the parameters should be varied to achieve the
desired response. You can then make adjustments to the
nominal values in the circuit file, and perform the
worst-case analysis again for a new set of gradients.
Parametric sweeps (.STEP), like the one
performed in the circuit file shown in
Figure 85, can be used to augment this
procedure.
Monte Carlo analysis
Monte Carlo (.MC) analysis may be helpful when
worst-case analysis cannot be used. Monte Carlo analysis
can often be used to verify or improve on worst-case
analysis results. Monte Carlo analysis randomly selects
possible parameter values, which can be thought of as
randomly selecting points in the parameter space. The
worst-case analysis assumes that the worst results occur
somewhere on the surface of this space, where parameters
(to which the output is sensitive) are at one of their
extreme values.
If this is not true, the Monte Carlo analysis may find a
point at which the results are worse. To try this, replace
.WC in the circuit file with .MC <#runs>, where <#runs> is
the number of simulations you want to perform. More
runs provide higher confidence results. The Monte Carlo
summary in the output file lists the runs in decreasing
order of collating function value.
To save disk space, do not specify any
OUTPUT options.
Next, add the following option to the .MC statement, and
simulate again.
OUTPUT LIST RUNS <worst_run#>
This performs only two simulations: the nominal and the
worst Monte Carlo run. The parameter values used
during the worst run are written to the output file, and the
results of both simulations are saved.
Using Monte Carlo analysis with YMAX is a good way to
obtain a conservative guess at the maximum possible
deviation from nominal, since worst-case analysis usually
cannot provide this information.
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Chapter 12 Monte Carlo and sensitivity/worst-case analyses
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Part four
Viewing results
Part four describes the ways to view simulation results.
•
Chapter 13, Analyzing waveforms, describes how to
perform graphical waveform analysis of simulation
results.
•
Chapter 14, Other output options, describes the special
symbols you can place on your schematic to generate
additional information to the PSpice output file and
PSpice window.
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Analyzing waveforms
13
Chapter overview
This chapter describes how to perform graphical
waveform analysis of simulation results in PSpice. This
chapter includes the following:
•
Overview of waveform analysis on page 13-320
•
Setting up waveform analysis on page 13-324
•
Viewing waveforms on page 13-327
•
Analog example on page 13-341
•
User interface features for waveform analysis on
page 13-344
•
User interface features for waveform analysis on
page 13-344
•
Tracking simulation messages on page 13-354
•
Trace expressions on page 13-356
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Chapter 13 Analyzing waveforms
Overview of waveform analysis
You can use the waveform analysis features of PSpice to
visually analyze and interactively manipulate the
waveform data produced by circuit simulation.
PSpice uses high-resolution graphics so you can view the
results of a simulation both on the screen and in printed
form. On the screen, waveforms appear as plots displayed
in Probe windows within the PSpice workspace.
In effect, waveform analysis is a software oscilloscope.
Performing a PSpice simulation corresponds to building
or changing a breadboard, and performing waveform
analysis corresponds to looking at the breadboard with an
oscilloscope.
With waveform analysis you can:
•
View simulation results in multiple Probe windows
•
Compare simulation results from multiple circuit
designs in a single Probe window
•
Display simple voltages, currents, and noise data
•
Display complex arithmetic expressions that use the
basic measurements
•
Display Fourier transforms of voltages and currents,
or of arithmetic expressions involving voltages and
currents
•
Add text labels and other annotation symbols for
clarification
PSpice generates two forms of output: the simulation
output file and the waveform data file. The calculations
and results reported in the simulation output file act as an
audit trail of the simulation. However, the graphical
analysis of information in the waveform data file is the
most informative and flexible method for evaluating
simulation results.
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Overview of waveform analysis
Elements of a plot
A single plot consists of the analog (lower) area and the
digital (upper) area.
digital
area
analog
area
Figure 91 Analog and digital areas of a plot.
You can display multiple plots at a time. If you display
only analog waveforms, the entire plot will be an analog
area. Likewise, if you display only digital waveforms, the
entire plot will be a digital area.
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Chapter 13 Analyzing waveforms
Elements of a Probe window
A Probe window is a separately managed waveform
display area. A Probe window can include multiple
analog and digital plots. Figure 92 shows two plots
displayed together.
From the View menu, choose Toolbar to
display orhide the toolbar.
Because a Probe window is a window object, you can
minimize and maximize windows, or move and scale the
windows, within the PSpice workspace. A toolbar can be
displayed in the Probe window and applies to the active
Probe window.
window A
window B
(active)
Figure 92 Two Probe windows.
You can display information from one or more waveform
data files in one Probe window. After the first file is
loaded, load other files into the same Probe window by
appending them in PSpice.
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Overview of waveform analysis
Managing multiple Probe windows
You can open any number of Probe windows. Each Probe
window is a tab on the worksheet displayed in the middle
of the workspace.
The same waveform data file can be displayed in more
than one Probe window. You can tile the windows to
compare data.
Only one Probe window is active at any given time,
identified by a highlighted title bar or a topmost tab.
Menu, keyboard, and mouse operations affect only the
active Probe window. You can switch to another Probe
window by clicking another tab or title bar.
Printing multiple windows
You can print all or selected Probe windows, with up to
nine windows on a single page. When you choose Print
from the File menu, a list of all open Probe windows
appears. Each Probe window is identified by the unique
identifier in parentheses in its title bar.
The arrangement of Probe windows on the page can be
customized using the Page Setup dialog box. You can
print in either portrait (vertical) or landscape (horizontal)
orientation. You can also use Print Preview to view all of
the Probe windows as they will appear when printed.
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Chapter 13 Analyzing waveforms
Setting up waveform analysis
Setting up colors
You can configure Probe display and print colors in:
For information on how to use the available
colors and color order in a Probe window,
see Configuring trace color
schemes on page 13-326.
•
The configuration file, PSPICE.INI
•
The Probe Options dialog box
Editing display and print colors in the PSPICE.INI
file
In the PSPICE.INI file, you can control the following print
and display color settings for Probe windows:
Colors for all items are specified as
<item name>=<color>. The item names
and what they represent are listed in
Table 1.
Here are the color names you can specify:
brightcyan
brightblue
brightgreen
brightred
•
The colors used to display traces
•
The colors used for the Probe window foreground and
background
•
The order colors are used to display traces
•
The number of colors used to display traces
To edit display and print colors in the PSPICE.INI file
After editing PSPICE.INI, you must restart PSpice before your
changes will take effect.
Note
brightmagenta
brightwhite
brightyellow
darkcyan
darkblue
1
In a standard text editor (such as Notepad), open
PSPICE.INI. (This file is normally located in the
C:\Windows directory.)
2
Scroll to the [PROBE DISPLAY COLORS] or
[PROBE PRINTER COLORS] section of the file.
3
darkgray darkgreen
darkmagenta
darkred
darkpink
lightgreen
lightblue
lightgray green
magenta
mustard
orange
Add or modify a color entry. See Table 1 on
page 13-325 for a description of color entries and their
default values. Valid item names include:
pink
purple
red
•
BACKGROUND
brown
blue
cyan
•
FOREGROUND
white
black
yellow
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Setting up waveform analysis
•
TRACE_1 through TRACE_12
4
If you added or deleted trace number entries, set
NUMTRACECOLORS=n to the new number of traces,
where n is between 1 and 12. This item represents the
number of trace colors displayed on the screen or
printed before the color order repeats.
5
Save the file.
Table 1
Default waveform viewing colors.
Item Name
Description
Default
BACKGROUND
specifies the color of
window background
BLACK
FOREGROUND
specifies the default
color for items not
explicitly specified
WHITE
TRACE_1
specifies the first color
used for trace display
BRIGHTGREEN
TRACE_2
specifies the second
color used for trace
display
BRIGHTRED
TRACE_3
specifies the third color
used for trace display
BRIGHTBLUE
TRACE_4
specifies the fourth
color used for trace
display
BRIGHTYELLOW
TRACE_5
specifies the fifth color
used for trace display
BRIGHTMAGENTA
TRACE_6
specifies the sixth color
used for trace display
BRIGHTCYAN
When you want to copy Probe plots to the
clipboard and then paste them into a black
and white document, choose the Change All
Colors to Black option under Foreground in
the Copy to Clipboard–Color Filter dialog
box (from the Window menu, choose Copy
to Clipboard).
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Chapter 13 Analyzing waveforms
Configuring trace color schemes
For information on what the default
available colors and color order are and
how to change them, see Editing
display and print colors in the
PSPICE.INI file on page 13-324.
In the Probe Options dialog box, you can set options for
how the available colors and the color order specified in
the PSPICE.INI file are used to display the traces in a
Probe window. You can use:
•
a different color for each trace
•
the same color for all the traces that belong to the same
y-axis
•
the available colors in sequence for each y-axis
•
the same color for all the traces that belong to the same
waveform data file
To configure trace color schemes in the Probe Options dialog box
1
From the Tools menu, choose Options to display the
Probe Options dialog box.
2
Under Trace Color Scheme, choose one of the
following options:
Table 2
PSpice saves the selected color scheme for
future waveform analyses.
326
3
Choose this option...
To do this...
Normal
Use a different color for each trace (for
up to 12 traces, depending on the
number of colors set in the PSPICE.INI
file).
Match Axis
Use the same color for all the traces
that belong to the same y-axis. The title
of the axis (by default, 1, 2, etc.) is the
same color as its traces.
Sequential Per Axis
Use the available colors in sequence for
each y-axis.
Unique by File
Use the same color for all the traces in
one Probe window that belong to the
same waveform data file.
Click OK.
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Viewing waveforms
Viewing waveforms
If you are using Capture, you can either view waveforms
automatically after you run a simulation, or you can
monitor the progress of the simulation as it is running.
Setting up waveform display from Capture
You can configure the way you want to view the
waveforms in PSpice by defining display settings in the
Probe Window tab in the Simulation Settings dialog box.
You do not need to exit PSpice if you are
finished examining the simulation results
for one circuit and want to begin a new
simulation from within Capture. However,
PSpice unloads the old waveform data file
for a circuit each time that you run a new
simulation of the circuit. After the
simulation is complete, the new or updated
waveform data file is loaded for viewing.
The display settings in the Probe Window tab are
explained in the following table.
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Chapter 13 Analyzing waveforms
Table 3
This setting...
Enables this type of waveform display...
Display Probe
window when
profile is opened.
Waveforms are displayed only when a
.DAT file is opened from within PSpice.
Display Probe
window... during
simulation.
Waveforms are displayed as the
simulation progresses (“marching
waveforms”).
Display Probe
window... after
simulation has
completed.
Waveforms are displayed only after the
full simulation has completed and all
data has been calculated.
Show... all markers
on open schematics.
Waveforms are displayed for those nets
that have markers attached in the
schematic.
Show... last plot.
Waveforms are displayed according to
the last display configuration that was
used in the Probe window.
Viewing waveforms while simulating
While a simulation is in progress, you can monitor the
results for the data section being written by PSpice. This
function is only available when the Display Probe
window during simulation option is enabled in the Probe
Window tab of the Simulation Settings dialog box.
To monitor results during a simulation
If you open a new Probe window (from the
Window menu, choose New Window) while
monitoring the data, the new window also
starts in monitor mode because it is
associated with the same waveform data
file.
328
1
From Capture’s PSpice menu, choose Edit Simulation
Settings to display the Simulation Settings dialog box.
2
Click the Probe Window tab.
3
Select Display Probe window and then click during
simulation.
4
Click OK to close the Simulation Settings dialog box.
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Viewing waveforms
5
From the PSpice menu, choose Run to start the
simulation.
One Probe window is displayed in monitor mode.
6
During a multi-run simulation (such as
Monte Carlo, parametric, or temperature),
PSpice displays only the data for the most
recent run in the Probe window.
Do one of the following to select the waveforms to be
monitored:
•
From PSpice’s Trace menu, choose Add, and enter
one or more trace expressions.
•
From Capture’s PSpice menu, point to Markers,
then choose and place one or more markers.
The Probe window monitors the waveforms for as
long as the most recent data section is being written.
After that data section is finished, the window
changes to manual mode. To see the full set of runs,
you must update the display by using the Add Trace
command under the Trace menu.
or press I
For more information, see Using
schematic page markers to add
t
13 331
Configuring update intervals
You can define the frequency at which PSpice updates the
waveform display as follows:
•
At fixed time intervals (every n sec)
•
According to the percentage of simulation completed
(every n %), where n is user-defined
The default setting (Auto) updates traces each time PSpice
gets new data from a simulation.
To change the update interval
1
From the Tools menu, choose Options.
2
In the Auto-Update Interval frame, choose the interval
type (sec or %), then type the interval in the text box.
Interacting with waveform analysis during
simulation
The functions that change the x-axis domain (that set a
new x-axis variable) can not be accessed while the
simulation is running. If you have enabled the display of
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Chapter 13 Analyzing waveforms
waveforms during simulation and wish to reconfigure the
x-axis settings (as explained below), you must wait until
the simulation run has finished.
The following table shows how to enable the functions
that change the x-axis domain.
Table 4
Enable this function...
By doing this...
Fast Fourier
transforms
1
From the Plot menu, choose Axis
Settings.
2
In the Processing Options frame, select
Fourier.
1
From the Plot menu, choose Axis
Settings.
2
In the Processing Options frame, select
Performance Analysis.
1
From the Plot menu, choose Axis
Settings, then click the X Axis tab.
2
Click the Axis Variable button.
3
In the X Axis Variable dialog box,
specify a new x-axis variable.
1
From the Trace menu, select Eval Goal
Function.
2
In the Evaluate Goal Function(s) dialog
box, specify a goal function.
1
From the File menu, choose
Append Waveform (.DAT).
2
Select a .DAT file to append.
Performance
analysis
New x-axis variable
Goal function
evaluation
Load a completed
data section
Pausing a simulation and viewing waveforms
You can pause a simulation to analyze waveforms before
the simulation is finished. After you pause the simulation,
you can either resume the simulation or end it.
To pause a simulation
330
1
From PSpice’s Simulation menu, choose Pause.
2
In the Probe window, view the waveforms generated
before you paused the simulation.
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Viewing waveforms
3
Do one of the following:
•
From the Simulation menu, choose Run to resume
the simulation.
•
From the Simulation menu, choose Stop to stop the
simulation.
Using schematic page markers to add traces
You can place markers on a schematic page to identify the
points where you want to see waveform results displayed.
You can place markers:
•
Before simulation, to limit results written to the
waveform data file and automatically display those
traces in PSpice.
•
During or after simulation, with PSpice running, to
automatically display traces in the active Probe
window.
See Trace expressions on
page 13-356 for ways to add traces
within PSpice.
The color of the marker you place is the same as its
corresponding waveform analysis trace. If you change the
color of the trace, the color of the marker on the schematic
page changes accordingly.
The Markers submenu also provides options for
controlling the display of marked results in PSpice, after
initial marker placement, and during or after simulation.
To place markers on a schematic page
1
From Capture’s PSpice menu, point to Markers, then
choose the marker type you want to place. (Some of
the markers are from the Advanced submenu.)
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Chapter 13 Analyzing waveforms
Table 5
Waveform
Markers menu command Advanced submenu command
voltage
Voltage Level
voltage
differential
Voltage Differential not required
current
Current Into Pin
not required
digital signal
Voltage Level
not required
dB*
Advanced
db Magnitude of Voltage
db Magnitude of Current
phase*
Advanced
Phase of Voltage
Phase of Current
group delay*
Advanced
Group Delay of Voltage
Group Delay of Current
real*
Advanced
Real Part of Voltage
Real Part of Current
imaginary*
Advanced
Imaginary Part of Voltage
Imaginary Part of Current
not required
* You can use these markers instead of the built-in functions provided in
output variable expressions (see Table 12 on page 13-364 ).
However, these markers are only available after defining a simulation
profile for an AC Sweep/Noise analysis.
The color of the marker is the same as its
corresponding waveform analysis trace. If
you change the color of the trace, the color
of the marker changes accordingly.
2
Point to the wires or pins you wish to mark and click
to place the chosen markers.
3
Right-click and select End Mode to stop placing
markers.
4
If you have not simulated the circuit yet, from the
PSpice menu, choose Run.
To hide or delete marked results
1
332
From Capture’s PSpice menu, point to Markers, then
choose one of the following:
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Viewing waveforms
Table 6
Choose this option...
To do this...
Hide All
Hide traces in the waveform analysis
display for all markers placed on any
page or level of the schematic.
Delete All
Remove all markers from the schematic
and all corresponding traces from the
waveform analysis display.
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Chapter 13 Analyzing waveforms
Limiting waveform data file size
When PSpice performs a simulation, it creates a waveform
data file. The size of this file for a transient analysis is
roughly equal to:
(# transistors)·(# simulation time points)·24 bytes
The size for other analysis types is about 2.5 times smaller.
For long runs, especially transient runs, this can generate
waveform data files that are several megabytes in size.
Even if this does not cause a problem with disk space,
large waveform data files take longer to read in and take
longer to display traces on the screen.
You can limit waveform data file size by:
•
placing markers on your schematic before simulation
and having PSpice restrict the saved data to these
markers only
•
excluding data for internal subcircuits
•
suppressing simulation output
Limiting file size using markers
One reason that waveform data files are large is that, by
default, PSpice stores all net voltages and device currents for
each step (for example, time or frequency points).
However, if you have placed markers on your schematic
prior to simulation, PSpice saves only the results for the
marked wires and pins.
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Viewing waveforms
To limit file size using markers
1
From Capture’s PSpice menu, choose Edit Simulation
Settings to display the Simulation Settings dialog box.
2
Click the Data Collection tab.
3
In the Schematic/Circuit Data frame, choose At
Markers only and click OK.
4
From the PSpice menu, point to Markers, then choose
the marker type you want to place.
5
Point to the wires or pins you wish to mark and click
to place the chosen markers.
6
Right-click and select End Mode to stop placing
markers.
7
From the PSpice menu, choose Run to start the
simulation.
The color of the marker on the schematic
page is the same as its corresponding
waveform analysis trace. If you change the
color of the trace, the color of the marker
changes accordingly.
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Chapter 13 Analyzing waveforms
Limiting file size by excluding internal subcircuit
data
By default, PSpice saves data for all internal nodes and
devices in subcircuit models in a design. You can exclude
data for internal subcircuit nodes and devices.
To limit file size by excluding data for internal subcircuits
1
From PSpice’s Simulation menu, choose Edit
Simulation Settings to display the Simulation Settings
dialog box.
2
Click the Data Collection tab.
3
In the Schematic/Circuit Data frame, choose All but
internal subcircuit data, then click OK.
4
From the PSpice menu, choose Run to start the
simulation.
Limiting file size by suppressing the first part
of simulation output
Suppressing part of the data run also limits
the size of the PSpice output file.
336
Long transient simulations create large waveform data
files because PSpice stores many data points. You can
suppress a part of the data from a transient run by setting
the simulation analysis to start the output at a time later
than 0. This does not affect the transient calculations
Pspug.book Page 337 Wednesday, November 11, 1998 1:14 PM
Viewing waveforms
themselves—these always start at time 0. This delay only
suppresses the output for the first part of the simulation.
To limit file size by suppressing the first part of transient
simulation output
1
From Capture’s PSpice menu, choose Edit Simulation
Settings to display the Simulation Settings dialog box.
2
Click the Analysis tab.
3
From the Analysis type list, select the
Time Domain (Transient) option.
4
In the Start saving data after text box, type a delay
time.
5
Click OK to close the Simulation Settings dialog box.
6
From the PSpice menu, choose Run to start the
simulation.
The simulation begins, but no data is stored until after
the delay has elapsed.
Using simulation data from multiple files
You can load simulation data from multiple files into the
same Probe window by appending waveform data files.
When more than one waveform data file is loaded, you
can add traces using all loaded data, data from only one
file, or individual data sections from one or more files.
Appending waveform data files
To append a waveform data file
1
In PSpice, from the File menu, choose
Append Waveform (.DAT).
2
Select a *.DAT file to append, and click OK.
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Chapter 13 Analyzing waveforms
3
4
If the file has multiple sections of data for the selected
analysis type, the Available Sections dialog box
appears. Do one of the following:
•
Click the sections you want to use.
•
Click the All button to use all sections.
Click OK.
Adding traces from specific loaded waveform data
files
If two or more waveform data files have identical
simulation output variables, trace expressions that
include those variables generate traces for each file.
However, you can specify which waveform data file to
use in the trace expression. You can also determine which
waveform data file was used to generate a specific trace.
To add a trace from a specific loaded waveform data file
or press UI
The Simulation Output Variables list in the
Add Traces dialog box contains the output
variables for all loaded waveform data
files.
1
In PSpice, from the Trace menu, choose Add Trace to
display the Add Traces dialog box.
2
In the Trace Expression text box, type an expression
using the following syntax:
[email protected]
where n is the numerical order (from left to right) of
the waveform data file as it appears in the PSpice title
bar, or
Example: To plot the V(1) output for data
section 1 from the second data file loaded,
type the following trace expression:
[email protected]@fn
V(1)@[email protected]
You can also use the name of the loaded
data file to specify it. For example, to plot
the V(1) output for all data sections of a
loaded data file, MYFILE.DAT, type the
following trace expression:
V(1)@"MYFILE.DAT"
where s is a specific data section of a specific
waveform data file.
3
To identify the source file for an individual trace
1
trace symbols
Figure 93 Trace legend symbols.
338
Click OK.
In the trace legend, double-click the symbol for the
trace you want to identify (Figure 93).
The Section Information dialog box appears,
containing the trace name and—if there is more than
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Viewing waveforms
one waveform data file loaded in the plot—the full
path for the file from which the trace was generated.
Also listed is information about the simulation that
generated the waveform data file and the number of
data points used (Figure 94).
Figure 94 Section information message box.
Saving simulation results in ASCII format
The default waveform data file format is binary. However,
you can save the waveform data file in the Common
Simulation Data Format (CSDF) instead.
Warning: Data files saved in the CSDF
format are two or more times the size of
binary files.
When you first open a CSDF data file,
PSpice converts it back to the .DAT format.
This conversion takes two or more times as
long as opening a .DAT file. PSpice saves
the new .DAT file for future use.
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Chapter 13 Analyzing waveforms
To save simulation results in ASCII format
1
From PSpice’s Simulation menu, choose Edit Profile to
display the Simulation Settings dialog box.
2
Click the Data Collection tab.
3
Select Save data in the CSDF format (.CSD).
4
Click OK.
PSpice writes simulation results to the waveform data
file in ASCII format (as *.CSD instead of *.DAT),
following the CSDF convention.
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Analog example
Analog example
In this section, basic techniques for performing waveform
analysis are demonstrated using the analog circuit
EXAMPLE.OPJ.
The example project EXAMPLE.OPJ is
provided with your OrCAD programs.
When shipped, EXAMPLE.OPJ is set up with
multiple analyses. For this example, the AC
sweep, DC sweep, Monte Carlo/worst-case,
and small-signal transfer function analyses
have been disabled. The specification for
each of these disabled analyses remains
intact. To run them from Capture in the
future, from the PSpice menu, choose Edit
Simulation Settings and enable the
analyses.
Figure 95 Example schematic EXAMPLE.OPJ.
Running the simulation
The simulation is run with the Bias Point Detail,
Temperature, and Transient analyses enabled. The
temperature analysis is set to 35 degrees. The transient
analysis is setup as follows:
Print Step
Final Time
Enable Fourier
Center Frequency
Output Vars
20ns
1000ns
selected
1Meg
V(OUT2)
To start the simulation
1
From Capture’s File menu, point to Open and choose
Project.
2
Open the following project in your OrCAD program
installation directory:
Note When you run a Fourier analysis
using PSpice as specified in this example,
PSpice writes the results to the PSpice
output file (*.OUT). You can also use Probe
windows to display the Fourier transform of
any trace expression by using the FFT
capability in PSpice. To find out more, refer
to PSpice A/D online Help.
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Chapter 13 Analyzing waveforms
\PSPICE\SAMPLES\ANASIM\EXAMPLE\
EXAMPLE.OPJ
If PSpice is set to show traces for all
markers on startup, you will see the
V(OUT1) and V(OUT2) traces when the
Probe window displays. To clear these
traces from the plot, from the Trace menu,
choose Delete All Traces.
3
From the PSpice menu, choose Run to start the
simulation.
PSpice generates a binary waveform data file containing
the results of the simulation. A new Probe window
appears with the waveform data file EXAMPLE.DAT
already loaded (Figure 96).
Figure 96 Waveform display for EXAMPLE.DAT.
Because this sample project was set up as a transient
analysis type, the data currently loaded are the results of
the transient analysis.
Note
342
In this sample, the voltage markers for OUT1 and OUT2 are already
placed in the design. If the markers are not placed prior to
simulating, you can display the waveforms later, as explained
below in Displaying voltages on nets.
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Analog example
Displaying voltages on nets
After selected an analysis, voltages on nets and currents
into device pins can be displayed in the Probe windows
using either schematic markers or output variables (as
will be demonstrated in this example).
To display the voltages at the OUT1 and OUT2 nets using output
variables
1
From the Trace menu, choose Add Trace to display the
Add Traces dialog box.
press UI
The Simulation Output Variables frame displays a list
of valid output variables.
2
Click V(OUT1) and V(OUT2), then click OK. The
Probe window should look similar to Figure 96.
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Chapter 13 Analyzing waveforms
User interface features for
waveform analysis
PSpice provides direct manipulation techniques and
shortcuts for analyzing waveform data. These techniques
are described below.
Shortcut keys
Many of the menu commands in PSpice
have equivalent keyboard shortcuts. For
instance, after placing a selection rectangle
in the analog portion of the plot, you can
type C+A instead of choosing Area
from the View menu. For a list of shortcut
keys, search on Keyboard Shortcuts in
PSpice Help.
Zoom regions
PSpice provides a direct manipulation method for
marking the zoom region in the analog area of the plot.
To zoom in or out
1
or
Do one of the following on the toolbar:
•
Click the View In toolbar button to zoom in by a
factor of 2 around the point you specify.
•
Click the View Out toolbar button to zoom out by
a factor of 2 around the point you specify.
To zoom in the analog area using the mouse
Click anywhere on the plot to remove the
selection rectangle without zooming.
1
Drag the mouse pointer to make a selection rectangle
as shown below.
selection rectangle (analog)
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User interface features for waveform analysis
2
From the View menu, point to Zoom, then choose
Area.
PSpice changes the plot to display the region within
the selection rectangle.
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Chapter 13 Analyzing waveforms
Scrolling traces
By default, when a plot is zoomed, standard scroll bars
appear to the right or at the bottom of the plot area as
necessary. These can be used to pan through the data. You
can configure scroll bars so they are always present or are
never displayed.
To configure scroll bars
1
In PSpice, from the Tools menu, choose Options.
2
In the Use Scroll Bars frame, choose one of the scroll
bars options, as described below.
Table 1
Choose this option...
To do this...
Auto
Have scroll bars appear when a plot
is zoomed or when additional traces
are displayed in the plot but are not
visible (default).
Never
Never display scroll bars. This mode
provides maximum plot size and is
useful on VGA and other low
resolution displays.
Always
Display scroll bars at all times.
However, they are disabled if the
corresponding axis is full scale.
Modifying trace expressions and labels
For information about adding labels
(including text, line, poly-line, arrow, box,
circle, ellipse, and mark), refer to the
online Help in PSpice.
346
You can modify trace expressions, text labels, and ellipse
labels that are currently displayed within the Probe
window, thus eliminating the need to delete and recreate
any of these objects.
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User interface features for waveform analysis
To modify trace expressions
1
Click the trace name to select it (selection is indicated
by a color change).
2
From the Edit menu, choose Modify Object.
3
In the Modify Trace dialog box, edit the trace
expression just as you would when adding a trace.
To modify text and ellipse labels
1
Click the text or ellipse to select it (selection is
indicated by a color change).
2
From the Edit menu, choose Modify Object.
3
Edit the label by doing one of the following:
•
In the Ellipse Label dialog box, change the
inclination angle.
•
In the Text Label dialog box, change the text label.
You can also double-click the trace name to
modify the trace expression.
For more information on adding traces, see
Adding traces from specific
loaded waveform data files on
page 13-338 and To add traces
using output variables on
page 13-356.
You can also double-click a text or ellipse
label to modify it.
Moving and copying trace names and expressions
Trace names and expressions can be selected and moved
or copied, either within the same Probe window or to
another Probe window.
To copy or move trace names and expressions
1
Click one or more (V+click) trace names. Selected
trace names are highlighted.
2
From the Edit menu, choose Copy or Cut to save the
trace names and expressions to the clipboard. Cut
removes trace names and traces from the Probe
window.
3
In the Probe window where traces are to be added, do
one of the following:
•
To add trace names to the end of the currently
displayed set, choose Paste from the Edit menu.
or
or press C+v
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Chapter 13 Analyzing waveforms
•
When adding a trace to a Probe window,
you can make the trace display name
different from the trace expression:
1 From the Trace menu, choose Add
Trace.
2 In the Trace Expression text box, enter
a trace expression using the syntax:
Here are some considerations when copying or moving
trace names and expressions into a different Probe
window:
•
If the new Probe window is reading the same
waveform data file, the copied or moved trace names
and expressions display traces that are identical to the
original selection set.
•
If the new Probe window is reading a different
waveform data file, the copied or moved names and
expressions display different traces generated from
the new data.
trace_expression[;display_name]
3 Click OK.
To add traces before a currently displayed trace
name, select the trace name and then choose Paste
from the Edit menu.
For example, suppose two waveform data files,
MYSIM.DAT and YOURSIM.DAT each contain a V(2)
waveform. Suppose also that two Probe windows are
currently displayed where window A is loaded with
MYSIM.DAT, and window B is loaded with
YOURSIM.DAT.
When V(2) is copied from window A to window B, the
trace looks different because it is determined by data
from YOURSIM.DAT instead of MYSIM.DAT.
Copying and moving labels
For information about adding labels
(including text, line, poly-line, arrow, box,
circle, ellipse, and mark), refer to the
online Help in PSpice.
or
Labels can be selected and moved or copied, either within
the same Probe window or to another Probe window.
To copy labels
1
Select one or more (V+click) labels, or select multiple
labels by drawing a selection rectangle. Selected labels
are highlighted.
2
From the Edit menu, choose Copy or Cut to save the
labels to the clipboard.
Cut removes labels from the Probe window.
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User interface features for waveform analysis
3
Switch to the Probe window where labels are to be
added, and from the Edit menu, choose Paste.
4
Click on the new location to place the labels.
press C+v
To move labels
1
Select one or more (V+click) labels, or select multiple
labels by drawing a selection rectangle. Selected labels
are highlighted.
2
Move the labels by dragging them to a new location.
Tabulating trace data values
You can generate a table of data points reflecting one or
more traces in the Probe window and use this information
in a document or spreadsheet.
To view the trace data values table
1
Select one or more (V+click) trace names. Selected
trace names are highlighted.
2
From the Edit menu, choose Copy or Cut to save the
trace data point values to the Clipboard.
or
Cut removes traces from the Probe window.
3
In Clipboard Viewer, from the Display menu, choose
either Text or OEM Text.
To export the data points to other applications
1
Select one or more (V+click) trace names. Selected
trace names are highlighted.
2
From the Edit menu, choose Copy or Cut to save the
trace data point values to the Clipboard.
Saving the data directly to a file from
Clipboard Viewer can create superfluous
data at the beginning of the file.
or
Cut removes traces from the Probe window.
3
Paste the data from the Clipboard into a text editor, a
spreadsheet program, or a technical computing
program (such as Mathcad).
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Chapter 13 Analyzing waveforms
4
Save the file.
Using cursors
When one or more traces are displayed, you can use
cursors to display the exact coordinates of two points on
the same trace, or points on two different traces. In
addition, differences are shown between the
corresponding coordinate values for the two cursors.
Displaying cursors
To display both cursors
press C+S+C
You can move the cursor box any where
over the Probe window by dragging the box
to another location.
1
From the Trace menu, point to Cursor, then choose
Display.
The Probe Cursor window appears, showing the
current position of the cursor on the x-axis and y-axis.
As you move the cursors, the values in the cursor box
change.
In the analog area of the plot (if any), both cursors are
initially placed on the trace listed first in the trace
legend. The corresponding trace symbol is outlined
with a dashed line.
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User interface features for waveform analysis
Moving cursors
To move cursors along a trace using menu commands
1
From the Trace menu, point to Cursor, then choose
Peak, Trough, Slope, Min, Max, Point, or Search.
For more information about the cursor
commands, refer to the online Help in
PSpice.
To move cursors along a trace using the mouse
1
Use the right and left mouse buttons as described in
Table 2 below.
Table 2
Mouse actions for cursor control
Click this...
To do this with the cursors...
For a family of curves (such as from a
nested DC sweep), you can use the mouse
or the arrow keys to move the cursor to one
of the other curves in the family. You can
also click the desired curve.
cursor assignment
Left-click the analog trace
symbol.
Associate the first cursor with
the selected trace.
Right-click the analog trace
symbol.
Associate the second cursor
with the selected trace.
cursor movement
Left-click in the display area.
Move the first cursor to the
closest trace segment at the
X position.
Right-click in the display
area.
Move the second cursor to
the closest trace segment at
the X position.
To move cursors along a trace using the keyboard
1
Use key combinations as described in Table 3 below.
Table 3
Key combinations for cursor control
Us this key combination...
To do this with the cursors...
C+l and C+r
Change the trace associated with the first
cursor.
V+C+l and
V+C+r
Change the trace associated with the
second cursor.
l and r
Move the first cursor along the trace.
V+l and V+r
Move the second cursor along the trace.
To place a label, click Plot, point to Label
and then choose the desired type of object
you want to place.
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Chapter 13 Analyzing waveforms
Table 3
Key combinations for cursor control (continued)
Us this key combination...
To do this with the cursors...
h
Move the first cursor to the beginning of
the trace.
V+h
Move the second cursor to the beginning
of the trace.
e
Move the first cursor to the end of the
trace.
V+e
Move the second cursor to the end of the
trace.
Example: using cursors
Figure 97 shows both cursors on the V(1) waveform in the
analog area of the plot.
digital
signal
w/cursors
cursor 1
results
cursor 2
results
analog
waveform
w/cursors
Figure 97 Cursors positioned on a trough and peak of V(1)
To position a cursor on the next trough of a
waveform, from the Trace menu, point to
Cursor, then choose Trough.
To position a cursor on the next peak of a
waveform, from the Trace menu, point to
Cursor, then choose Peak.
For more information about cursors, refer
to the online Help in PSpice.
352
Cursor 1 is positioned on the first trough (dip) of the V(1)
waveform. Cursor 2 is positioned on the second peak of
the same waveform. In the Probe Cursor window, cursor
1 and cursor 2 coordinates are displayed (A1 and A2,
respectively) with their difference shown in the bottom
line (dif). The logic state of the Out signal is also displayed
to the right of the cursor coordinates.
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User interface features for waveform analysis
The mouse buttons are also used to associate each cursor
with a different trace by clicking appropriately on either
the analog trace symbol in the legend. These are outlined
in the pattern corresponding to the associated cursor’s
crosshair pattern. Given the example in Figure 97,
right-clicking the V(2) symbol will associate cursor 2 with
the V(2) waveform. The analog legend now appears as
shown below.
cursor 1
cursor 2
The Probe Cursor window also updates the A2
coordinates to reflect the X and Y values corresponding to
the V(2) waveform.
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Chapter 13 Analyzing waveforms
Tracking simulation messages
PSpice provides explanatory messages for errors that
occur during simulation with their corresponding
waveforms. You can view messages from:
•
the Simulation Message Summary dialog box, or
•
the waveform display.
Message tracking from the message summary
A message summary is available for simulations where
diagnostics have been logged to the waveform data file.
You can display the message summary:
•
When loading a waveform data file (click OK when
the Simulation Errors dialog box appears).
•
Anytime by choosing Simulation Messages from the
View menu.
The Simulation Message Summary dialog box
The Simulation Message Summary dialog box lists
message header information. You can filter the messages
displayed in the list by selecting a severity level from the
Minimum Severity Level drop-down menu. Messages are
categorized (in decreasing order of severity) as FATAL,
SERIOUS, WARNING, or INFO (informational).
Example: If you select WARNING as the
minimum severity level, the Simulation
Message Summary dialog box will display
WARNING, SERIOUS, and FATAL messages.
354
When you select a severity level, the Message Summary
displays only those messages with the chosen severity or
higher. By default, the minimum severity level displayed is
SERIOUS.
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Tracking simulation messages
To display waveforms associated with messages
1
In the Simulation Message Summary dialog box,
double-click a message.
For most message conditions, a Probe window
appears that contains the waveforms associated with
the simulation condition, along with detailed message
text.
Persistent hazards
If a PERSISTENT HAZARD message is displayed, two
plots appear (see Figure 98), containing the following:
•
the waveforms that initially caused the timing
violation or hazard (lower plot)
•
the primary outputs or internal state devices to which
the condition has propagated (upper plot)
Figure 98 Waveform display for a persistent hazard.
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Chapter 13 Analyzing waveforms
Message tracking from the waveform
Trace segments with associated diagnostics are displayed
in the foreground color specified in your PSPICE.INI file.
This color is different from those used for standard state
transitions.
To display explanatory message text
1
Double-click within the tagged region of a trace.
Trace expressions
Traces are referred to by output variable names. Output
variables are similar to the PSpice output variables
specified in the Simulation Settings dialog box for noise,
Monte Carlo, worst-case, transfer function, and Fourier
analyses. However, there are additional alias forms that
are valid for trace expressions. Both forms are discussed
here.
To add traces using output variables
1
From the Trace menu, choose Add Trace to display the
Add Traces dialog box.
2
Construct a trace expression using any combination of
these controls:
You can display a subset of the available
simulation output variables by selecting or
clearing the variable type check boxes in
the Simulation Output Variables frame.
Variable types not generated by the circuit
simulation are dimmed.
For more information about trace
expressions, see Analog trace
expressions on page 13-364.
356
3
•
In the Simulation Output Variables frame, click
output variables.
•
In the Functions or Macros frame, select operators,
functions, constants, or macros.
•
In the Trace Expression text box, type in or edit
output variables, operators, functions, constants,
or macros.
If you want to change the name of the trace expression
as it displays in the Probe window, use the following
syntax:
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Trace expressions
trace expression;display name
4
Click OK.
Basic output variable form
This form is representative of those used for specifying
some PSpice analyses.
<output>[A C suffix](<name>[,name])
Table 4
This placeholder...
Means this...
<output>
type of output quantity: V for voltage
or I for current
[A C suffix ]*
quantity to be reported for an AC
analysis. For a list of valid AC suffixes,
see Table 8 on page 13-361
<name>[,name]
specifies either the net or (+ net, - net)
pair for which the voltage is to be
reported, or the device for which a
current is reported, where:
•
net specifies either the net or pin
id (<fully qualified device
name>:<pin name>)
• device name specifies the fully
qualified device name; for a list of
device types, see Table 9 on
page 13-361 and Table 10 on
page 13-362
A fully qualified device name consists of the
full hierarchical path followed by the
device’s reference designator. For
information about syntax, see the voltage
output variable naming rules.
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Chapter 13 Analyzing waveforms
Output variable form for device terminals
This form can only be specified for trace expressions. The
primary difference between this and the basic form is that
the terminal symbol appears before the net or device name
specification (whereas the basic form treats this as the pin
name within the pin id).
<output>[terminal]*[A C suffix](<name>[,name])
Table 5
This placeholder...
Means this...
<output>
type of output quantity: V for voltage, I
for current, or N for noise
[terminal]*
one or more terminals for devices with
more than two terminals; for a list of
terminal IDs, see Table 10 on
page 13-362
[A C suffix ]*
quantity to be reported for an AC
analysis; for a list of valid AC suffixes,
see Table 8 on page 13-361
<name>[,<name>]
)
net, net pair, or fully qualified device
name; f or a list of device types, see
Table 9 on page 13-361 and Table 10
on page 13-362
Table 6 on page 13-358 summarizes the valid output
formats. Table 7 on page 13-360 provides examples of
equivalent output variables. Note that some of the output
variable formats are unique to trace expressions.
Table 6
Output variable formats
Format
Meaning
Voltage variables
358
V[ac](< +analog net > [,< -analog net
>])
Voltage between +
and - analog net ids
V<pin name>[ac](< device >)
Voltage at pin name
of a device
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Trace expressions
Table 6
Output variable formats (continued)
Format
Meaning
V< x >[ac](< 3 or 4-terminal device >) Voltage at
non-grounded
terminal x of a
3 or 4-terminal
device
V< z >[ac](< transmission line device
>)
Voltage at end z of a
transmission line
device (z is either
A or B)
Current variables
I[ac](< device >)
Current into a device
I< x >[ac](< 3 or 4-terminal device >)
Current into terminal
x of a 3 or 4-terminal
device
I< z >[ac](< transmission line device
>)
Current into end z of
a transmission line
device (z is either
A or B)
Sweep variables
< DC sweep variable >
name of any variable
used in the DC
sweep analysis
FREQUENCY
AC analysis sweep
variable
TIME
transient analysis
sweep variable
Noise variables
V[db](ONOISE)
total RMS-summed
noise at output net
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Chapter 13 Analyzing waveforms
Table 6
Output variable formats (continued)
Format
Meaning
V[db](INOISE)
total equivalent noise
at input source
NTOT(ONOISE)
sum of all noise
contributors in the
circuit
N< noise type >(< device name >)
contribution from
noise type of device
name to the total
output noise*
* See Table 11 on page 13-363 for a complete list of noise types by
device type. For information about noise output variable equations, the units
used to represent noise quantities in trace expressions, and a noise analysis
example, see Analyzing Noise in the Probe window on
page 9-245.
Table 7
360
Examples of output variable formats
A basic form
An alias equivalent Meaning
V(NET3,NET2)
(same)
voltage between analog nets
labeled NET3 and NET2
V(C1:1)
V1(C1)
voltage at pin1 of capacitor C1
VP(Q2:B)
VBP(Q2)
phase of voltage at base of
bipolar transistor Q2
V(T32:A)
VA(T32)
voltage at port A of transmission
line T32
I(M1:D)
ID(M1)
current through drain of
MOSFET device M1
VIN
(same)
voltage source named VIN
FREQUENCY
(same)
AC analysis sweep variable
NFID(M1)
(same)
flicker noise from MOSFET M1
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Trace expressions
Table 8
Output variable AC suffixes
Suffix
Meaning of output variables
none
magnitude
DB
magnitude in decibels
G
group delay (-dPHASE/dFREQUENCY)
I
imaginary part
M
magnitude
P
phase in degrees
R
real part
Table 9
Device names for two-terminal device types
Two-terminal device type*
Device type letter
capacitor
C
diode
D
voltage-controlled voltage source**
E
current-controlled current source**
F
voltage-controlled current source**
G
current-controlled voltage source**
H
independent current source
I
inductor
L
resistor
R
voltage-controlled switch**
S
independent voltage source
V
current-controlled switch**
W
* The pin name for two-terminal devices is either 1 or 2.
** The controlling inputs for these devices are not considered terminals.
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Chapter 13 Analyzing waveforms
Table 10
Terminal IDs by three & four-terminal device type
Three & four-terminal device type
Device type
letter
Terminal IDs
GaAs MOSFET
B
D (drain)
G (gate)
S (source)
Junction FET
J
D (drain)
G (gate)
S (source)
MOSFET
M
D (drain)
G (gate)
S (source)
B (bulk, substrate)
Bipolar transistor
Q
C (collector)
B (base)
E (emitter)
S (substrate)
transmission line
T
A (near side)
B (far side)
IGBT
Z
C (collector)
G (gate)
E (emitter)
362
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Trace expressions
Table 11
Noise types by device type
Device type
Noise types*
Meaning
B (GaAsFET)
FID
RD
RG
RS
SID
TOT
flicker noise
thermal noise associated with RD
thermal noise associated with RG
thermal noise associated with RS
shot noise
total noise
D (diode)
FID
RS
SID
TOT
flicker noise
thermal noise associated with RS
shot noise
total noise
J (JFET)
FID
RD
RG
RS
SID
TOT
flicker noise
thermal noise associated with RD
thermal noise associated with RG
thermal noise associated with RS
shot noise
total noise
M (MOSFET)
FID
RB
RD
RG
RS
SID
TOT
flicker noise
thermal noise associated with RB
thermal noise associated with RD
thermal noise associated with RG
thermal noise associated with RS
shot noise
total noise
Q (BJT)
FIB
RB
RC
RE
SIB
SIC
TOT
flicker noise
thermal noise associated with RB
thermal noise associated with RC
thermal noise associated with RE
shot noise associated with base current
shot noise associated with collector current
total noise
R (resistor)
TOT
total noise
Iswitch
TOT
total noise
Vswitch
TOT
total noise
* These variables report the contribution of the specified device’s noise to the total output noise in units of V 2/Hz. This means
that the sum of all device noise contributions is equal to the total output noise in V2/Hz, NTOT(ONOISE).
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Chapter 13 Analyzing waveforms
Analog trace expressions
Trace expression aliases
Analog trace expressions vary from the output variables
used in simulation analyses because analog net values can
be specified by:
<output variable>[;display name]
as opposed to the <output variable> format used in
analyses. With this format, the analog trace expression can
be displayed in the analog legend with an optional alias.
Arithmetic functions
Arithmetic expressions of analog output variables use the
same operators as those used in simulation analyses (by
means of part property definitions in Capture). You can
also include intrinsic functions in expressions. The
intrinsic functions available for trace expressions are
similar to those available for PSpice math expressions, but
with some differences, as shown in Table 12. A complete
list of PSpice arithmetic functions can be found in Table 10
on page 3-71.
Table 12
364
Analog arithmetic functions for trace expressions
Probe
function
Description
Available in
PSpice?
ABS(x)
|x|
YES
SGN(x)
+1 (if x>0), 0 (if x=0), -1 (if x<0)
YES
SQRT(x)
x1/2
YES
EXP(x)
e
YES
LOG(x)
ln(x)
YES
LOG10(x)
log(x)
YES
M(x)
magnitude of x
YES
P(x)
phase of x (degrees)
YES
R(x)
real part of x
YES
IMG(x)
imaginary part of x
YES
x
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Trace expressions
Table 12
Analog arithmetic functions for trace expressions
Probe
function
Description
Available in
PSpice?
G(x)
group delay of x (seconds)
NO
PWR(x,y)
|x|y
YES
SIN(x)
sin(x)
YES
COS(x)
cos(x)
YES
TAN(x)
tan(x)
YES
ATAN(x)
ARCTAN(x)
tan-1 (x)
YES
d(x)
derivative of x with respect to the
x-axis variable
YES*
s(x)
integral of x over the range of the
x-axis variable
YES**
AVG(x)
running average of x over the range of
the x-axis variable
NO
AVGX(x,d)
running average of x from
X_axis_value(x)-d to X_axis_value(x)
NO
RMS(x)
running RMS average of x over the
range of the x-axis variable
NO
DB(x)
magnitude in decibels of x
NO
MIN(x)
minimum of the real part of x
NO
MAX(x)
maximum of the real part of x
NO
* In PSpice, this function is called DDT(x).
** In PSpice, this function is called SDT(x).
Note
For AC analysis, PSpice uses complex arithmetic to evaluate trace
expressions. If the result of the expression is complex, then its
magnitude is displayed.
Rules for numeric values suffixes
Explicit numeric values are entered in trace expressions in
the same form as in simulation analyses (by means of part
properties in Capture), with the following exceptions:
•
Suffixes M and MEG are replaced with m (milli, 1E-3)
and M (mega, 1E+6), respectively.
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Chapter 13 Analyzing waveforms
•
MIL and mil are not supported.
Example: V(5) and v(5) are equivalent in
trace expressions.
•
With the exception of the m and M scale suffixes,
PSpice is not case sensitive; therefore, upper and
lower case characters are equivalent.
Example: The quantities 2e-3, 2mV, and
.002v all have the same numerical value.
For axis labeling purposes, PSpice
recognizes that the second and third forms
are in volts, whereas the first is
dimensionless.
Unit suffixes are only used to label the axis; they never
affect the numerical results. Therefore, it is always safe to
leave off a unit suffix.
PSpice also knows that W=V·A, V=W/A,
and A=W/V. So, if you add this trace:
V(5)*ID(M13)
the axis values are labeled with W.
For a demonstration of analog trace
presentation, see Analog example on
page 13-341.
366
The units to use for trace expressions are shown in
Table 13.
Table 13
Output units for trace expressions
Symbol
Unit
V
volt
A
amps
W
watt
d
degree (of phase)
s
second
Hz
hertz
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Other output options
14
Chapter overview
This chapter describes how to output results in addition to
those normally written to the data file or output file.
•
Viewing analog results in the PSpice window on
page 14-368 explains how to monitor the numerical
values for voltages or currents on up to three nets in
your circuit as the simulation proceeds.
•
Writing additional results to the PSpice output file on
page 14-369 explains how to generate additional line
plots and tables of voltage and current values to the
PSpice output file.
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Chapter 14 Other output options
Viewing analog results in the
PSpice window
Capture provides a special WATCH1 part that lets you
monitor voltage values for up to three nets in your
schematic as a DC sweep, AC sweep or transient analysis
proceeds. Results are displayed in PSpice.
To display voltage values in the PSpice window
If the results move outside of the specified
bounds, PSpice pauses the simulation so
that you can investigate the behavior.
1
Place and connect a WATCH1 part (from the PSpice
library SPECIAL.OLB) on an analog net.
2
Double-click the WATCH1 part instance to display the
Parts spreadsheet.
3
In the ANALYSIS property column, type DC, AC, or
TRAN (transient) for the type of analysis results you
want to see.
4
Enter values in the LO and HI properties columns to
define the lower and upper bounds, respectively, on
the values you expect to see on this net.
5
Repeat steps 1 through 4 for up to two more WATCH1
instances.
6
Start the simulation.
For example, in the schematic fragment shown below,
WATCH1 parts are connected to the Mid and Vcc nets.
After starting the simulation, PSpice displays voltages on
the Mid and Vcc nets.
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Writing additional results to the PSpice output file
Writing additional results to the
PSpice output file
Capture provides special parts that let you save additional
simulation results to the PSpice output file as either
line-printer plots or tables.
To view the PSpice output file after having
run a simulation:
1 From the Simulation menu, choose
Examine Output.
Generating plots of voltage and current values
You can generate voltage and current line-printer plots for
any DC sweep, AC sweep, or transient analysis.
To generate plots of voltage or current to the output file
1
Place and connect any of the following parts (from the
PSpice library SPECIAL.OLB).
Table 14
Use this part...
To plot this...
VPLOT1
Voltage on the net that the part
terminal is connected to.
VPLOT2
Voltage differential between the two
nets that the part terminals are
connected to.
IPLOT
Current through a net. (Insert this part
in series, like a current meter.)
2
Double-click the part instance to display the Parts
spreadsheet.
3
Click the property name for the analysis type that you
want plotted: DC, AC, or TRAN.
4
In the columns for the analysis type that you want
plotted (DC, AC or TRAN), type any non-blank value
such as Y, YES or 1.
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Chapter 14 Other output options
If you do not enable a format, PSpice
defaults to MAG.
5
6
If you selected the AC analysis type, enable an output
format:
a
Click the property name for one of the following
output formats: MAG (magnitude), PHASE,
REAL, IMAG (imaginary), or DB.
b
Type any non-blank value such as Y, YES or 1.
c
Repeat the previous steps (a) and (b) for as many
AC output formats as you want to see plotted.
Repeat steps 2 through 5 for any additional analysis
types you want plotted.
If you do not enable an analysis type, PSpice reports the transient
results.
Note
Generating tables of voltage and current values
You can generate tables of voltage and current values on
nets for any DC sweep, AC sweep, or transient analysis.
To generate tables of voltage or current to the output file
1
Place and connect any of the following parts (from the
PSpice library SPECIAL.OLB).
Table 15
Use this part...
To tabulate this...
VPRINT1
Voltage on the net that the part
terminal is connected to.
VPRINT2
Voltage differential between the two
nets that the part terminals are
connected to.
IPRINT
Current through a cut in the net.
(Insert this part in series, like a current
meter.)
2
370
Double-click the part instance to display the Parts
spreadsheet.
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Writing additional results to the PSpice output file
3
Click the property name for the analysis type that you
want tabulated: DC, AC, or TRAN.
4
In the columns for the analysis type that you want
plotted (DC, AC or TRAN), type any non-blank value
such as Y, YES or 1.
5
If you selected the AC analysis type, enable an output
format.
6
Note
a
Click the property name for one of the following
output formats: MAG (magnitude), PHASE,
REAL, IMAG (imaginary), or DB.
b
Type any non-blank value such as Y, YES or 1.
c
Repeat the previous steps (a) and (b) for as many
AC output formats as you want to see tabulated.
If you do not enable a format, PSpice
defaults to MAG.
Repeat steps 2 through 5 for any additional analysis
types you want plotted.
If you do not enable an analysis type, PSpice reports the transient
results.
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Chapter 14 Other output options
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Setting initial state
A
Appendix overview
This appendix includes the following sections:
•
Save and load bias point on page A-374
•
Setpoints on page A-376
•
Setting initial conditions on page A-378
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Chapter A Setting initial state
Save and load bias point
If the circuit uses high gain components, or
if the circuit’s behavior is nonlinear around
the bias point, this feature is not useful.
Save Bias Point and Load Bias Point are used to save and
restore bias point calculations in successive PSpice
simulations. Saving and restoring bias point calculations
can decrease simulation times when large circuits are run
multiple times and can aid convergence.
Save/Load Bias Point affect the following types of
analyses:
•
transient
•
DC
•
AC
Save bias point
Save bias point is a simulation control function that allows
you to save the bias point data from one simulation for use
as initial conditions in subsequent simulations. Once bias
point data is saved to a file, you can use the load bias point
function to use the data for another simulation.
To use save bias point
See Setting up analyses on
page 7-197 for a description of the
Analysis Setup dialog box.
374
1
In the Simulation Settings dialog box, click the
Analysis tab.
2
Under Options, select Save Bias Point.
3
Complete the Save Bias Point dialog box.
4
Click OK.
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Save and load bias point
Load bias point
Load bias point is a simulation control function that
allows you to set the bias point as an initial condition. A
common reason for giving PSpice initial conditions is to
select one out of two or more stable operating points (set
or reset for a flip-flop, for example).
To use load bias point
1
Run a simulation using the Save Bias Point option in
the Simulation Settings dialog box.
2
Before running another simulation, click the Analysis
tab in the Simulation Settings dialog box.
3
Under Options, select Load Bias Point.
4
Specify a bias point file to load. Include the path if the
file is not located in your working directory, or use the
Browse button to find the file.
5
Click OK.
See Setting up analyses on
page 7-197 for a description of the
Analysis Setup dialog box.
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Chapter A Setting initial state
Setpoints
Pseudocomponents that specify initial conditions are
called setpoints. These apply to the analog portion of your
circuit.
Figure A-1 Setpoints.
The example in Figure A-1 includes the following:
IC1
a one-pin symbol that allows you to set
the initial condition on a net for both
small-signal and transient bias points
IC2
a two-pin symbol that allows you to set
initial condition between two nets
Using IC symbols sets the initial conditions for the bias
point only. It does not affect the DC sweep. If your circuit
design contains both an IC symbol and a NODESET
symbol for the same net, the NODESET symbol is ignored.
To specify the initial condition, edit the value of the
VALUE property to the desired initial condition. PSpice
attaches a voltage source with a 0.0002 ohm series
resistance to each net to which an IC symbol is connected.
The voltages are clamped this way for the entire bias point
calculation.
NODESET1 is a one-pin symbol which helps calculate the
bias point by providing a initial guess for some net.
NODESET2 is a two-pin symbol which helps calculate the
bias point between two nets. Some or all of the circuit’s
nets may be given an initial guess. NODESET symbols are
effective for the bias point (both small-signal and transient
bias points) and for the first step of the DC sweep. It has
no effect during the rest of the DC sweep or during the
transient analysis itself.
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Setpoints
Unlike the IC pseudocomponents, NODESET provides
only an initial guess for some net voltages. It does not
clamp those nodes to the specified voltages. However, by
providing an initial guess, NODESET symbols may be
used to break the tie (in a flip-flop, for instance) and make
it come up in a desired state. To guess at the bias point,
enter the initial guess in the Value text box for the VALUE
property. PSpice attaches a voltage source with a 0.0002
ohm series resistance to each net to which an IC symbol is
connected.
These pseudocomponents are netlisted as PSpice .IC and
.NODESET commands. Refer to these commands in the
online OrCA D PSpice A /D Reference Manual for more
information. Setpoints can be created for inductor
currents and capacitor voltages using the IC property
described in Setting initial conditions on page A-378.
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Chapter A Setting initial state
Setting initial conditions
The IC property allows initial conditions to be set on
capacitors and inductors. These conditions are applied
during all bias point calculations. However, if you select
the Skip Initial Transient Solution check box in the
Transient Analysis Setup dialog box, the bias point
calculation is skipped and the simulation proceeds
directly with transient analysis at TIME=0. Devices with
the IC property defined start with the specified voltage or
current value; however, all other such devices have an
initial voltage or current of 0.
Note
See Setpoints on page A-376 for
more information about IC1 and IC2.
Skipping the bias point calculation can make the transient analysis
subject to convergence problems.
Applying an IC property for a capacitor has the same
effect as applying one of the pseudocomponents IC1 or
IC2 across its nodes. PSpice attaches a voltage source with
a 0.002 ohm series resistance in parallel with the capacitor.
The IC property allows the user to associate the initial
condition with a device, while the IC1 and IC2
pseudocomponents allow the association to be with a
node or node pair.
In the case of initial currents through inductors, the
association is only with a device, and so there are no
corresponding pseudocomponents. The internal
implementation is analogous to the capacitor. PSpice
attaches a current source with a 1 Gohm parallel resistance
in series with the inductor.
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Convergence and “time step
too small errors”
B
Appendix overview
This appendix discusses common errors and convergence
problems in PSpice.
•
Introduction on page B-380
•
Bias point and DC sweep on page B-385
•
Transient analysis on page B-388
•
Diagnostics on page B-393
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Chapter B Convergence and “time step too small errors”
Introduction
In order to calculate the bias point, DC sweep and
transient analysis for analog devices PSpice must solve a
set of nonlinear equations which describe the circuit's
behavior. This is accomplished by using an iterative
technique—the Newton-Raphson algorithm—which
starts by having an initial approximation to the solution
and iteratively improves it until successive voltages and
currents converge to the same result.
In a few cases PSpice cannot find a solution to the
nonlinear circuit equations. This is generally called a
“convergence problem” because the symptom is that the
Newton-Raphson repeating series cannot converge onto a
consistent set of voltages and currents. The following
discussion gives some background on the algorithms in
PSpice and some guidelines for avoiding convergence
problems.
The AC and noise analyses are linear and do
not use an iterative algorithm, so the
following discussion does not apply to
them.
The transient analysis has the additional possibility of
being unable to continue because the time step required
becomes too small from something in the circuit moving
too fast. This is also discussed below.
Newton-Raphson requirements
The Newton-Raphson algorithm is guaranteed to converge
to a solution. However, this guarantee has some
conditions:
1
The nonlinear equations must have a solution.
2
The equations must be continuous.
3
The algorithm needs the equations' derivatives.
4
The initial approximation must be close enough to the
solution.
Each of these can be taken in order. Remember that the
PSpice algorithms are used in computer hardware that
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Introduction
has finite precision and finite dynamic range that produce
these limits:
•
Voltages and currents in PSpice are limited to +/-1e10
volts and amps.
•
Derivatives in PSpice are limited to 1e14.
•
The arithmetic used in PSpice is double precision and
has 15 digits of accuracy.
Is there a solution?
Yes, for any physically realistic circuit. However, it is not
difficult to set up a circuit that has no solution within the
limits of PSpice numerics. Consider, for example, a
voltage source of one megavolt connected to a resistor of
one micro-ohm. This circuit does not have a solution
within the dynamic range of currents (+/- 1e10 amps).
Here is another example:
V1
1,
D1
1,
.MODEL
0
5v
0
DMOD
DMOD(IS=1e-16)
The problem here is that the diode model has no series
resistance. It can be shown that the current through a
diode is:
I = IS*eV/(N*k*T)
To find out more about the diode equations,
refer to the A nalog Devices chapter in
the online OrCAD PSpice A/D Reference
Manual.
N defaults to one and k*T at room temperature is about
.025 volts. So, in this example the current through the
diode would be:
I = 1e-16*e200 = 7.22e70 amps
This circuit also does not have a solution within the limits
of the dynamic range of PSpice. In general, be careful of
components without limits built into them. Extra care is
needed when using the expressions for controlled sources
(such as for behavioral modeling). It is easy to write
expressions with very large values.
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Chapter B Convergence and “time step too small errors”
Are the Equations Continuous?
The device equations built into PSpice are continuous. The
functions available for behavioral modeling are also
continuous (there are several functions, such as int(x),
which cannot be added because of this). So, for physically
realistic circuits the equations can also be continuous.
Exceptions that come are usually from exceeding the
limits of the numerics in PSpice. This example tries to
approximate an ideal switch using the diode model:
.MODEL DMOD(IS=1e-16 N=1e-6)
The current through this diode is:
I = 1e-16*eV/(N*.025) = 1e-16*eV/25e-9
Avoid unrealistic model parameters.
Behavioral modeling expressions need
extra care.
Because the denominator in the exponential is so small,
the current I is essentially zero for V < 0 and almost
infinite for V > 0. Even if there are external components
that limit the current, the “knee” of the diode's I-V curve
is so sharp that it is almost a discontinuity.
Are the derivatives correct?
The device equations built into PSpice include the
derivatives, and these are correct. Depending on the
device, the physical meaning of the derivatives is
small-signal conductance, transconductance or gain.
Unrealistic model parameters can exceed the limit of 1e14,
but it requires some effort. The main thing to look at is the
behavioral modeling expressions, especially those having
denominators.
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Introduction
Is the initial approximation close enough?
Newton-Raphson is guaranteed to converge only if the
analysis is started close to the answer. Also, there is no
measurement that can tell how close is close enough.
PSpice gets around this by making heavy use of
continuity. Each analysis starts from a known solution
and uses a variable step size to find the next solution. If the
next solution does not converge PSpice reduces the step
size, falls back and tries again.
Bias point
The hardest part of the whole process is getting started,
that is, finding the bias point. PSpice first tries with the
power supplies set to 100%. A solution is not guaranteed,
but most of the time the PSpice algorithm finds one. If not,
then the power supplies are cut back to almost zero. They
are cut to a level small enough that all nonlinearities are
turned off. When the circuit is linear a solution can be
found (very near zero, of course). Then, PSpice works its
way back up to 100% power supplies using a variable step
size.
Once a bias point is found the transient analysis can be
run. It starts from a known solution (the bias point) and
steps forward in time. The step size is variable and is
reduced as needed to find further solutions.
DC sweep
The DC sweep uses a hybrid approach. It uses the bias
point algorithm (varying the power supplies) to get
started. For subsequent steps it uses the previous solution
as the initial approximation. The sweep step is not
variable, however. If a solution cannot be found at a step
then the bias point algorithm is used for that step.
The whole process relies heavily on continuity. It also
requires that the circuit be linear when the supplies are
turned off.
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Chapter B Convergence and “time step too small errors”
STEPGMIN
An alterative algorithm is GMIN stepping. This is not
obtained by default, and is enabled by specifying the
circuit analysis option STEPGMIN (either using .OPTION
STEPGMIN in the netlist, or by making the appropriate
choice from the Analysis/Setup/Options menu). When
enabled, the GMIN stepping algorithm is applied after the
circuit fails to converge with the power supplies at 100
percent, and if GMIN stepping also fails, the supplies are
then cut back to almost zero.
GMIN stepping attempts to find a solution by starting the
repeating cycle with a large value of GMIN, initially
1.0e10 times the nominal value. If a solution is found at
this setting it then reduces GMIN by a factor of 10, and
tries again. This continues until either GMIN is back to the
nominal value, or a repeating cycle fails to converge. In
the latter case, GMIN is restored to the nominal value and
the power supplies are stepped.
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Bias point and DC sweep
Bias point and DC sweep
Power supply stepping
As previously discussed, PSpice uses a proprietary
algorithm which finds a continuous path from zero power
supplies levels to 100%. It starts at almost zero (.001%)
power supplies levels and works its way back up to the
100% levels. The minimum step size is 1e-6 (.0001%). The
first repeating series of the first step starts at zero for all
voltages.
Semiconductors
Model parameters
The first consideration for semiconductors is to avoid
physically unrealistic model parameters. Remember that
as PSpice steps the power supplies up it has to step
carefully through the turn on transition for each device. In
the diode example above, for the setting N=1e-6, the knee
of the I-V curve would be too sharp for PSpice to maintain
its continuity within the power supply step size limit of
1e-6.
Unguarded p-n junctions
A second consideration is to avoid “unguarded” p-n
junctions (no series resistance). The above diode example
also applies to the p-n junctions inside bipolar transistors,
MOSFETs (drain-bulk and source-bulk), JFETs and
GaAsFETs.
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Chapter B Convergence and “time step too small errors”
No leakage resistance
A third consideration is to avoid situations which could
have an ideal current source pushing current into a
reverse-biased p-n junction without a shunt resistance.
Since p-n junctions in PSpice have (almost) no leakage
resistance and would cause the junction's voltage to go
beyond 1e10 volts.
The model libraries which are part of PSpice follow these
guidelines.
Typos can cause unrealistic device parameters. The
following MOSFET:
M1 3, 2, 1, 0
MMOD
L=5 W=3
has a length of five meters and a width of three meters
instead of micrometers. It should have been:
M1 3, 2, 1, 0
MMOD
L=5u W=3u
PSpice flags an error for L too large, but cannot for W
because power MOSFETs are so interdigitated (a
zipper-like trace) that their effective W can be very high.
The LIST option can show this kind of problem. When the
devices are listed in the output file their values are shown
in scientific notation making it easy to spot unusual
values.
Switches
PSpice switches have gain in their transition region. If
several are cascaded then the cumulative gain can easily
exceed the derivative limit of 1e14. This can happen when
modeling simple logic gates using totem-pole switches
and there are several gates in cascaded in series. Usually a
cascade of two switches works but three or more can cause
trouble.
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Bias point and DC sweep
Behavioral modeling expressions
Range limits
Voltages and currents in PSpice are limited to the range
+/- 1e10. Care must be taken that the output of
expressions fall within this range. This is especially
important when one is building an electrical analog of a
mechanical, hydraulic or other type of system.
Source limits
Another consideration is that the controlled sources must
turn off when the supplies are almost 0 (.001%). There is
special code in PSpice which “squelches” the controlled
sources in a continuous way near 0 supplies. However,
care should still be taken using expressions that have
denominators. Take, for example, a constant power load:
GLOAD 3, 5
VALUE = {2Watts/V(3,5)}
The first repeating series starts with V(3,5) = 0 and the
current through GLOAD would be infinite (actually, the
code in PSpice which does the division clips the result to a
finite value). The “squelching” code is required to be a
smooth and well-behaved function.
Note
The “squelching” code cannot be “strong” enough to suppress
dividing by 0.
The result is that GLOAD does not turn off near 0 power
supplies. A better way is described in the application note
Modeling Constant Power Loads. The “squelching” code
is sufficient for turning off all expressions except those
having denominators. In general, though, it is good
practice to constrain expressions having the LIMIT
function to keep results within physically realistic
bounds.
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Chapter B Convergence and “time step too small errors”
Example: A first approximation to an opamp that has an
open loop gain of 100,000 is:
VOPAMP
3, 5
VALUE = {V(in+,in-)*1e5}
This has the undesirable property that there is no limit on
the output. A better expression is:
VOPAMP
3, 5 VALUE =
+ {LIMIT(V(in+,in-)*1e5,15v,-15v}
where the output is limited to +/- 15 volts.
Transient analysis
The transient analysis starts using a known solution - the
bias point. It then uses the most recent solution as the first
guess for each new time point. If necessary, the time step
is cut back to keep the new time point close enough that
the first guess allows the Newton-Raphson repeating
series to converge. The time step is also adjusted to keep
the integration of charges and fluxes accurate enough.
In theory the same considerations which were noted for
the bias point calculation apply to the transient analysis.
However, in practice they show up during the bias point
calculation first and, hence, are corrected before a
transient analysis is run.
The transient analysis can fail to complete if the time step
gets too small. This can have two different effects:
1
The Newton-Raphson iterations would not converge
even for the smallest time step size, or
2
Something in the circuit is moving faster than can be
accommodated by the minimum step size.
The message PSpice puts into the output file specifies
which condition occurred.
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Transient analysis
Skipping the bias point
The SKIPBP option for the transient analysis skips the bias
point calculation. In this case the transient analysis has no
known solution to start from and, therefore, is not assured
of converging at the first time point. Because of this, its use
is not recommended. It inclusion in PSpice is to maintain
compatibility with UC Berkeley SPICE. SKIPBP has the
same meaning as UIC in Berkeley SPICE. UIC is not
needed in order to specify initial conditions.
The dynamic range of TIME
TIME, the simulation time during transient analysis, is a
double precision variable which gives it about 15 digits of
accuracy. The dynamic range is set to be 15 digits minus
the number of digits of accuracy required by RELTOL.
For a default value of RELTOL = .001 (.1% or 3 digits) this
gives 15-3 = 12 digits. This means that the minimum time
step is the overall run time (TSTOP) divided by 1e12. The
dynamic range is large but finite.
It is possible to exceed this dynamic range in some
circuits. Consider, for example, a timer circuit which
charges up a 100uF capacitor to provide a delay of 100
seconds. At a certain threshold a comparator turns on a
power MOSFET. The overall simulation time is 100
seconds. For default RELTOL this gives us a minimum
time step of 100 picoseconds. If the comparator and other
circuitry has portions that switch in a nanosecond then
PSpice needs steps of less than 100 picoseconds to
calculate the transition accurately.
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Chapter B Convergence and “time step too small errors”
Failure at the first time step
If the transient analysis fails at the first time point then
usually there is an unreasonably large capacitor or
inductor. Usually this is due to a typographical error.
Consider the following capacitor:
C
1 3, 0 1Ouf
“1O” (has the letter O) should have been “10.” This
capacitor has a value of one farad, not 10 microfarads. An
easy way to catch these is to use the LIST option (on the
.OPTIONS command).
LIST
The LIST option can echo back all the devices into the
output file that have their values in scientific notation.
That makes it easy to spot any unusual values. This kind
of problem does not show up during the bias point
calculation because capacitors and inductors do not
participate in the bias point.
Similar comments apply to the parasitic capacitance
parameters in transistor (and diode) models. These are
normally echoed to the output file (the NOMOD option
suppresses the echo but the default is to echo). As in the
LIST output, the model parameters are echoed in scientific
notation making it easy to spot unusual values. A further
diagnostic is to ask for the detailed operating bias point
(.TRAN/OP) information.
.TRAN/OP
This lists the small-signal parameters for each
semiconductor device including the calculated parasitic
capacitances.
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Transient analysis
Parasitic capacitances
It is important that switching times be nonzero. This is
assured if devices have parasitic capacitances. The
semiconductor model libraries in PSpice have such
capacitances. If switches and/or controlled sources are
used, then care should be taken to assure that no sections
of circuitry can try to switch in zero time. In practice this
means that if any positive feedback loops exist (such as a
Schmidt trigger built out of switches) then such loops
should include capacitances.
Another way of saying all this is that during transient
analysis the circuit equations must be continuous over
time (just as during the bias point calculation the
equations must be continuous with the power supply
level).
Inductors and transformers
While the impedance of capacitors gets lower at high
frequencies (and small time steps) the impedance of
inductors gets higher.
Note
The inductors in PSpice have an infinite bandwidth.
Real inductors have a finite bandwidth due to eddy
current losses and/or skin effect. At high frequencies the
effective inductance drops. Another way to say this is that
physical inductors have a frequency at which their Q
begins to roll off. The inductors in PSpice have no such
limit. This can lead to very fast spikes as transistors (and
diodes) connected to inductors turn on and off. The fast
spikes, in turn, can force PSpice to take unrealistically
small time steps.
Note
OrCAD recommends that all inductors have a parallel resistor
(series resistance is good for modeling DC effects but does not limit
the inductor's bandwidth).
The parallel resistor gives a good model for eddy current
loss and limits the bandwidth of the inductor. The size of
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Chapter B Convergence and “time step too small errors”
resistor should be set to be equal to the inductor's
impedance at the frequency at which its Q begins to roll
off.
Example: A common one millihenry iron core inductor
begins to roll off at no less than 100KHz. A good resistor
value to use in parallel is then R = 2*π*100e3*.001 = 628
ohms. Below the roll-off frequency the inductor
dominates; above it the resistor does. This keeps the width
of spikes from becoming unreasonably narrow.
Bipolar transistors substrate junction
The UC Berkeley SPICE contains an unfortunate
convention for the substrate node of bipolar transistors.
The collector-substrate p-n junction has no DC component.
If the capacitance model parameters are specified (e.g.,
CJS) then the junction has (voltage-dependent)
capacitance but no DC current. This can lead to a sneaky
problem: if the junction is inadvertently forward-biased it
can create a very large capacitance. The capacitance goes
as a power of the junction voltage. Normal junctions
cannot sustain much forward voltage because a large
current flows. The collector-substrate junction is an
exception because it has no DC current.
If this happens it usually shows up at the first time step. It
can be spotted turning on the detailed operating point
information (.TRAN/OP) and looking at the calculated
value of CJS for bipolar transistors. The whole problem
can be prevented by using the PSpice model parameter
ISS. This parameter “turns on” DC current for the
substrate junction.
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Diagnostics
Diagnostics
If PSpice encounters a convergence problem it inserts into
the output file a message that looks like the following.
ERROR -- Convergence problem in transient analysis at Time =
Time step =
47.69E-15, minimum allowable step size =
7.920E-03
300.0E-15
These voltages failed to converge:
V(x2.23)
V(x2.25)
=
=
1230.23 / -68.4137
-1211.94 / 86.6888
These supply currents failed to converge:
I(X2.L1)
I(X2.L2)
=
=
-36.6259 / 2.25682
-36.5838 / 2.29898
These devices failed to converge:
X2.DCR3
X2.DCR4
x2.ktr
X2.Q1
X2.Q2
Last node voltages tried were:
NODE
VOLTAGE
NODE
VOLTAG
E
NODE
25.2000
(
3)
4.0000
(
(x2.23
)
1230.200
0
(X2.24)
9.1441
(X2.28
)
-206.610
0
(X2.29)
(X3.34
)
1.771E-0
6
(X3.35)
(
1)
VOLTAGE
NODE
0.0000
(
6)
25.2030
(x2.25
)
-1211.900
0
(X2.26)
256.970
0
75.487
0
(X2.30
)
-25.0780
(X2.31)
26.2810
1.0881
(X3.36
)
.4279
(X2.XU1.6
)
1.2636
4)
VOLTAGE
The message always includes the banner (ERROR -convergence problem ...) and the trailer (Last node
voltages tried were ...). It cannot include all three of
the middle blocks.
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Chapter B Convergence and “time step too small errors”
The Last node voltages tried... trailer shows the
voltages tried at the last Newton-Raphson iteration. If any
of the nodes have unreasonable large values this is a clue
that these nodes are related to the problem. “These
voltages failed to converge” lists the specific nodes which
did not settle onto consistent values. It also shows their
values for the last two iterations. “These supply currents
failed converge” does the same for currents through
voltage sources and inductors. If any of the listed numbers
are +/- 1e10 then that is an indication that the value is
being clipped from an unreasonable value. Finally, “These
devices failed to converge” shows devices whose terminal
currents or core fluxes did not settle onto consistent
values.
The message gives a clue as to the part of the circuit which
is causing the problem. Looking at those devices and/or
nodes for the problems discussed above is recommended.
394
Pspug.book Page 395 Wednesday, November 11, 1998 1:14 PM
Index
A
ABM
ABM part templates, 152
ABM.OLB, 149
basic controlled sources, 192
cautions and recommendations for simulation,
186
control system parts, 153
custom parts, 192
frequency domain device models, 181
frequency domain parts, 181, 187
instantaneous models, 176, 186
overview, 148
placing and specifying ABM parts, 150
PSpice A/D-equivalent parts, 174–175
signal names, 147
simulation accuracy, 191
syntax, 175
triode modeling example, 171
AC stimulus property, 234
AC sweep analysis, 196, 231–232
about, 232
displaying simulation results, 39
example, 37, 237
introduction, 4
noise analysis, 196, 241
setup, 37, 232, 235
stimulus, 233
treatment of nonlinear devices, 239
ACMAG stimulus property, 234
ACPHASE stimulus property, 234
adding a stimulus, 33
AGND ground part, 83
analog behavioral modeling, see ABM
analog parts
basic components (ABM), 153, 155
basic controlled sources (ABM), 192
behavioral, 66
bipolar transistors, 95, 204, 362–363
breakout, 65
capacitors, 202
Chebyshev filters, 153, 157, 190, 301
Darlington model transistors, 95
diodes, 95, 202, 363
expression parts (ABM), 154, 168
frequency table parts (ABM), 174, 183, 190
GaAsFET, 203, 362–363
IGBT, 95, 204, 362
inductors, 202
integrators and differentiators (ABM), 153, 160
JFET, 95, 203, 362–363
Pspug.book Page 396 Wednesday, November 11, 1998 1:14 PM
Index
Laplace transform (ABM), 154, 164, 174, 181, 187
limiters (ABM), 153, 156
math functions (ABM), 154, 167
mathematical expressions (ABM), 174
MOSFET, 95, 204, 362–363
nonlinear magnetic core, 95
opamp, 95
passive, 64
PSpice A/D-equivalent parts (ABM), 174
resistors, 203, 363
switch, 363
table look-up (ABM), 153, 160, 174, 179
transmission lines, 204, 362
vendor-supplied, 61
voltage comparator, 95
voltage reference, 95
voltage regulator, 95
analyses
AC sweep, 37, 196, 231–232
bias point detail, 22, 196
DC sensitivity, 196, 228
DC sweep, 26, 196, 214
execution order, 198
Fourier, 196
frequency response, 196
Monte Carlo, 196, 289
noise, 196, 241
overview, 3
parametric, 42, 196, 272
performance analysis, 49
sensitivity/worst-case, 196, 306
setup, 197
small-signal DC transfer, 196, 225
temperature, 196, 281
transient, 32, 196
types, 196
approximation, problems, 383
B
basic components (ABM), 153, 155
basic controlled sources (ABM), 192
behavioral modeling expressions, 387
behavorial parts, 66
bias point
convergence analysis, 389
save/restore, 374
skipping, 389
bias point detail analysis, 196
396
example, 22
introduction, 3
bipolar transistors, 95, 204, 362–363
problems, 392
Bode plot, 4, 40
C
capacitors, 202
Chebyshev filters, 153, 157, 190, 301
circuit file (.CIR), 10
simulating multiple circuits, 207
color settings for waveform analysis, 324
comparator, 95
continuous equations
problems, 382
control system parts (ABM), 153
controlled sources, 174, 192
convergence analysis
bias point, 389
convergence problems, 379
approximations, 383
behavioral modeling expressions, 387
bias point, 385
bipolar transistors, 392
continuous equations, 382
DC sweep, 385
derivatives, 382
diagnostics, 393
dynamic range of time, 389
inductors and transformers, 391
Newton-Raphson requirements, 380
parasitic capacitances, 391
semiconductors, 385
switches, 386
transient analysis, 388
Create Subcircuit command, 91, 115
current source, controlled, 174, 192
cursors, waveform analysis, 350
custom part creation for models, 133
using the Model Editor, 100, 131
D
Darlington model transistors, 95
DC analyses
displaying simulation results, 28
Pspug.book Page 397 Wednesday, November 11, 1998 1:14 PM
Index
see also DC sweep analysis, bias point detail
analysis, small-signal DC transfer
analysis, DC sensitivity analysis
DC sensitivity analysis, 196, 228
introduction, 3
DC stimulus property, 219
DC sweep analysis, 196, 214
about, 216
curve families, 221
example, 26
introduction, 3
nested, 219
setting up, 26
stimulus, 218
derivative
problems, 382
design
preparing for simulation, 9, 56
device noise, 242, 245
total, 245
diagnostic problems, 393
differentiators (ABM), 153, 160
digital parts
vendor-supplied, 61
digital simulation
waveform display, 344, 364
diodes, 95, 202, 363
dynamic range of time, 389
E
EGND ground part, 83
examples and tutorials
AC sweep analysis, 37, 237
analog waveform analysis, 339
bias point detail analysis, 22
DC sweep analysis, 26
example circuit creation, 16
frequency response vs. arbitrary parameter, 278
mixed analog/digital waveform analysis, 344
modeling a triode (ABM), 171
Monte Carlo analysis, 293
parametric analysis, 42
performance analysis, 49, 274
transient analysis, 32
using the Model Editor, 104, 114
worst-case analysis, 309
expression parts (ABM), 154, 168
expressions, 69–70
see also parameters
ABM, 174
functions, 71
specifying, 69
system variables, 73
waveform analysis, 364
F
files
generated by Capture, 10
user-configurable, 11
with simulation results, 14
flicker noise, 245
Fourier analysis, 196
introduction, 5
FREQUENCY output variable, 359
frequency response vs. arbitrary parameter, 278
frequency table parts (ABM), 174, 183, 190
functions
PSpice A/D, 71
waveform analysis, 364
G
GaAsFET, 203, 362–363
goal functions, 275
in performance analysis, 276
single data point, 276
grid spacing
part graphics, 136
part pins, 136
ground
missing, 83
missing DC path to, 84
parts, 60
group delay, 361
H
histograms, 301
hysteresis curves, 266
I
IAC stimulus part, 233
IC (property), 378
ICn initial conditions parts, 376
397
Pspug.book Page 398 Wednesday, November 11, 1998 1:14 PM
Index
IDC stimulus part, 74, 218
IGBT, 95, 204, 362
imaginary part, 361
include files, 11
configuring, 13, 120
with model definitions, 121
inductors, 202
problems, 391
initial conditions, 374, 378
input noise, total, 245
instance models
and the Model Editor, 101, 112
changing model references, 117
editing, 103
reusing, 118
saving for global use instead
using the Model Editor, 113
integrators (ABM), 153, 160
IPLOT (write current plot part), 369
IPRINT (write current table part), 370
ISRC stimulus part, 74, 218, 233
ISTIM stimulus part, 76
J
JFET, 95, 203, 362–363
L
Laplace transform parts (ABM), 154, 164, 174, 181, 187–
188
libraries
configuring, 120
footprint, 13
model, 88
package, 13
part (.OLB), 13
searching for models, 121
see also model libraries
Library List, using the, 63
limiters (ABM), 153, 156
M
magnetic core, nonlinear, 95
magnitude, 361
markers, 334
displaying traces, 28
398
for limiting waveform data file size, 334
for waveform display, 331
math function parts (ABM), 154, 167
mathematical expressions (ABM), 174
mixed analog/digital circuits
waveform display, 344, 364
Model Editor
about, 10, 110
analyzing model parameter effects, 97
changing
.MODEL definitions, 110
.SUBCKT definitions, 111
model names, 111
creating parts for models, 100, 131
custom, 133
example, 114
fitting models, 97
starting stand-alone, 99
startng from the schematic page editor, 101
supported device types, 95
testing and verifying models, 96
tutorial, 104
using data sheet information, 96
viewing performance curves, 98
ways to use, 94
model editor
running from the
schematic page editor, 111
model libraries, 11, 88
adding to the configuration, 122
analog list of, 80
and duplicate model names, 122
configuration, 89
configured as include files, 121
configuring, 13, 81, 120
directory search path, 125
global vs. design, 89, 123
how PSpice searches them, 121
nested, 90
OrCAD-provided, 90
preparing for part creation, 130
search order, 121, 124
MODEL property, 87, 138
models
built-in, 2
changing associations to parts, 117
creating parts for
custom, 133
using the Model Editor, 100, 131
creating with the Model Editor, 110
Pspug.book Page 399 Wednesday, November 11, 1998 1:14 PM
Index
defined as
parameter sets, 87
subcircuits, 87, 115
global vs. design, 89
instance, 101, 112, 117–118
organization, 88
preparing for part creation, 130
saving as design
using the Model Editor, 101
saving as local
using the Model Editor, 111
testing/verifying (Model Editor-created), 96
tools to create, 91
ways to create/edit, 92
Monte Carlo analysis, 196, 289
collating functions, 287
histograms, 301
introduction, 7
model parameter values reports, 285
output control, 285
tutorial, 293
using the Model Editor, 114
waveform reports, 286
with temperature analysis, 288
MOSFET, 95, 204, 362–363
multiple y-axes, waveform analysis, 276
N
netlist
failure to netlist, 58
file (.NET), 10
Newton-Raphson requirements, 380
NODESETn initial conditions parts, 376
noise analysis, 196, 241
about, 4, 242
device noise, 242
flicker noise, 245
noise equations, 245
setup, 241, 243
shot noise, 245
thermal noise, 245
total output and input noise, 242
units of measure, 246
viewing results, 246
viewing simulation results, 245, 363
waveform analysis output variables, 245, 363
noise units, 246
non-causality, 188
nonlinear
magnetic core, 95
nonlinear devices
in AC sweep analysis, 239
O
opamp, 95
operators in expressions, 70
options
RELTOL, 191
output control parts, 60, 369
output file (.OUT), 24
control parts, 369
tables and plots, 369
output noise, total, 245
output variables
arithmetic expressions, 364
noise (waveform analysis), 245, 363
PSpice A/D, 199
waveform analysis, 356
waveform analysis functions, 364
P
PARAM global parameter part, 67
parameters, 67
parametric analysis, 196, 272
analyzing waveform families, 45
example, 42
frequency response vs. arbitrary parameter, 278
introduction, 6
performance analysis, 274
setting up, 43
temperature analysis, 196, 281
parasitic capacitance, 391
part wizard
using custom parts, 133
parts
creating for models
using the Model Editor, 100, 131
creating new stimulus parts, 259
editing graphics, 135
grid spacing
graphics, 136
pins, 136
ground, 60
non-simulation, 140
output control, 60
399
Pspug.book Page 400 Wednesday, November 11, 1998 1:14 PM
Index
pins, 82, 136
preparing model libraries for part creation, 130
properties for simulation, 139
saving as global
using the Model Editor, 100, 131
simulation control, 60
simulation properties, 129
stimulus, 60
ways to create for models, 129
AGND (ground), 83
BBREAK (GaAsFET), 65
behavioral, 66
breakout, 65
C (capacitor), 64
CBREAK (capacitor), 65
creating for models
custom parts, 133
using the Model Editor, 131
CVAR (capacitor), 64
D (diode), 64
DBREAK (diode), 65
EGND (ground), 83
finding, 62
IAC (AC stimulus), 233
ICn (initial conditions), 376
IDC (DC stimulus), 74, 218
ISRC (analog stimulus), 74, 218, 233
ISTIM (transient stimulus), 76
JBREAK (JFET), 65
K_LINEAR (transformer), 64
KBREAK (inductor coupling), 65
KCOUPLEn (coupled transmission line), 64
LBREAK (inductor), 65
MBREAK (MOSFET), 65
MODEL property, 138
NODESETn, 376
PARAM (global parameter), 67
passive, 64
QBREAK (bipolar transistor), 65
R (resistor), 64
RBREAK (resistor), 65
RVAR (resistor), 64
SBREAK (voltage-controlled switch), 65
T (ideal transmission line), 64
TBREAK (transmission line), 65
TEMPLATE property, 140
TnCOUPLEDx (coupled transmission line), 64
unmodeled, 79
VAC (AC stimulus), 75, 233
VDC (DC stimulus), 74–75
400
vendor-supplied, 61
VEXP (transient stimulus), 75
VPULSE (transient stimulus), 75
VPWL (transient stimulus), 75
VPWL_F_N_TIMES (transient stimulus), 76
VPWL_F_RE_FOREVER (transient stimulus), 75
VPWL_N_TIMES (transient stimulus), 76
VPWL_RE_FOREVER (transient stimulus), 75
VSFFM (transient stimulus), 76
VSIN (transient stimulus), 76
VSRC (analog stimulus), 74–75, 233
VSTIM (analog stimulus), 75
VSTIM (transient stimulus), 76
WBREAK (current-controlled switch), 65
XFRM_LINEAR (transformer), 64
XFRM_NONLINEAR (transformer), 65
ZBREAK (IGBT), 65
ABMn and ABMn/I (ABM), 154, 168
ABS (ABM), 154, 167
ARCTAN (ABM), 154, 167
ATAN (ABM), 154, 167
BANDPASS (ABM), 153, 158
BANDREJ (ABM), 153, 159
CONST (ABM), 153, 155
COS (ABM), 154, 167
DIFF (ABM), 153, 155
DIFFER (ABM), 153, 160
E (ABM controlled analog source), 192
EFREQ (ABM), 174, 183
ELAPLACE (ABM), 174, 181
EMULT (ABM), 174, 178
ESUM (ABM), 174, 178
ETABLE (ABM), 174, 179
EVALUE (ABM), 174, 176–177
EXP (ABM), 154, 167
F (ABM controlled analog source), 192
FTABLE (ABM), 153, 161
G (ABM controlled analog source), 192
GAIN (ABM), 153, 155
GFREQ (ABM), 174, 183
GLAPLACE (ABM), 174, 181
GLIMIT (ABM), 153, 156
GMULT (ABM), 174, 178
GSUM (ABM), 174, 178
GTABLE (ABM), 174, 179
GVALUE (ABM), 174, 176–177
H (ABM controlled analog source), 192
HIPASS (ABM), 153, 158
ICn (initial condition), 376
INTEG (ABM), 153, 160
Pspug.book Page 401 Wednesday, November 11, 1998 1:14 PM
Index
LAPLACE (ABM), 154, 164
LIMIT (ABM), 153, 156
LOG (ABM), 154, 167
LOG10 (ABM), 154, 167
LOPASS (ABM), 153, 157
MULT (ABM), 153, 155
NODESETn (initial bias point), 376
PWR (ABM), 154, 167
PWRS (ABM), 154, 167
SIN (ABM), 154, 167
SOFTLIM (ABM), 153, 156
SQRT (ABM), 154, 167
SUM (ABM), 153, 155
TABLE (ABM), 153, 160
TAN (ABM), 154, 167
performance analysis, 274
example, 49
goal functions, 275
phase, 361
plots in waveform analysis, 321
power supplies
analog, 74
Probe windows
plot update methods, 346
plots, 321–322
printing Probe windows, 323
scrolling, 346
setting colors, 324
trace data tables, 349
traces, displaying, 28
zoom regions, 344
properties (part) for simulation, 139
PSpice
default shortcut keys, 344
waveform analysis, 320
multiple y-axes, 276
PSpice A/D
about, 2
expressions, 69
functions, 71
output file (.OUT), 24, 369
output variables, 199
PSpice A/D-equivalent parts, 174–175
simulation status window, 208, 368
starting, 206
using with other programs, 9
viewing in-progress output values, 368
waveform data file (.DAT), 14
PSPICE.INI file, editing, 324
R
real part, 361
regulator, 95
RELTOL (simulation option), 191
resistors, 203, 363
S
schematic page editor
starting other tools from
Model Editor, 101, 111–112
scrolling, Probe windows, 346
semiconductor
problems, 385
shot noise, 245
simulation
about, 2
analysis
execution order, 198
setup, 197
types, 196
batch jobs, 207
bias point, 374
failure to start, 58
initial conditions, 374, 378
output file (.OUT), 24
setup checklist, 56
starting, 206
status window, 208
troubleshooting checklist, 58
simulation control parts, 60
ICn, 376
NODESETn (initial conditions), 376
PARAM, 67
small-signal DC transfer analysis, 196, 225
introduction, 3
Stimulus Editor, 33, 253
about, 9
creating new stimulus parts, 259
defining analog stimuli, 76
defining stimuli, 256
editing a stimulus, 260
manual stimulus configuration, 261
starting, 254
stimulus files, 253–254
stimulus files, 11
configuring, 13, 120
stimulus generation, 252
401
Pspug.book Page 402 Wednesday, November 11, 1998 1:14 PM
Index
manually configuring, 261
stimulus, adding, 33
AC sweep, 233
DC sweep, 218
for multiple analysis types, 77
transient (analog/mixed-signal), 252
subcircuits, 87
creating .SUBCKT definitions from designs, 91
creating .SUBCKT definitions from schematics,
115
tools to create, 91
ways to create/edit, 92
see also models
switch, 363
problems, 386
system variables in expressions, 73
T
table look-up parts (ABM), 153, 160, 174, 179
temperature analysis, 196, 281
introduction, 6
with statistical analyses, 288
TEMPLATE property, 140
and non-simulation parts, 140
examples, 143
naming conventions, 141
regular characters, 140
special characters, 142
thermal noise, 245
TIME (Probe output variable), 359
total noise, 242
circuit, 245
per device, 245
traces
adding, 28
direct manipulation, 344
displaying, 28, 35
markers, 334
output variables, 356
placing a cursor on, 30
transformer
problems, 391
transient analysis, 196
example, 32
Fourier analysis, 196
hysteresis curves, 266
internal time steps, 265
introduction, 5
402
overview, 250
problems, 388
setting up, 34
Stimulus Editor, 253
stimulus generation, 252
switching circuits, 266
transient response, 263
transistors, Darlington model, 95
transmission lines, 362
triode, 171
troubleshooting
checklist, 58
missing DC path to ground, 84
missing ground, 83
unconfigured libraries and files, 81
unmodeled parts, 79
unmodeled pins, 82
tutorials, see examples and tutorials
U
unmodeled
parts, 79
pins, 82
updating plots, 346
V
VAC stimulus part, 75, 233
variables in expressions, 73
VDC (DC stimulus), 218
VDC stimulus part, 74–75
vendor-supplied parts, 61
VEXP stimulus part, 75
voltage comparator, 95
voltage reference, 95
voltage regulator, 95
voltage source, controlled, 174, 192
VPLOTn (write voltage plot part), 369
VPRINTn (write voltage table part), 370
VPULSE stimulus part, 75
VPWL stimulus part, 75
VPWL_F_N_TIMES stimulus part, 76
VPWL_F_RE_FOREVER stimulus part, 75
VPWL_N_TIMES stimulus part, 76
VPWL_RE_FOREVER stimulus part, 75
VSFFM stimulus part, 76
VSIN stimulus part, 76
VSRC stimulus part, 74–75, 78, 218, 233
Pspug.book Page 403 Wednesday, November 11, 1998 1:14 PM
Index
VSTIM stimulus part, 33, 75–76
W
WATCH1 (view output variable part), 368
waveform analysis, 320
about, 8
adding traces, 28
cursors, 350
displaying simulation results, 28, 39
expressions, 364
functions, 364
hysteresis curves, 266
limiting waveform data file size, 334
multiple y-axes, 276
output variables, 356
for noise, 245, 363
performance analysis, 49, 274
placing a cursor on a trace, 30
plot, 321
printing Probe windows, 323
setting colors, 324
trace data tables, 349
traces, 334
traces, displaying, 344
traces, using output variables, 356
using markers, 331
waveform data file (.DAT), 14
waveform data file formats, 339
waveform families, 45, 221
waveform data file formats, 339
waveform families, displaying, 45
wavform analysis
arithmetic expressions, 364
worst-case analysis, 196, 306
collating functions, 287
example, 309
hints, 313
introduction, 7
model parameter values reports, 285
output control, 285
overview, 306
waveform reports, 286
with temperature analysis, 288
Z
zoom regions, Probe windows, 344
403
Pspug.book Page 404 Wednesday, November 11, 1998 1:14 PM
Index
404
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